refactor: Instance settings back to separate pages with sidebar sub-links

The continuous scroll was wrong for Instance — its sub-panels are
fundamentally different page types (user table, storage tool, bitrate
matrix, toggles). Revert to conditional rendering.

The hook now supports two modes:
- Scroll mode (default): smooth scroll + IntersectionObserver spy
- Tab mode (onNavigate callback): sidebar sub-links switch tabs

Instance uses tab mode. The scroll-spy infrastructure remains for
future panels that benefit from it (e.g. Account sections).

Also reverts GeneralPanel to sticky save bar since it's on its own
page again with no overlap risk.

packages/web/src/components/modals/instanceSettingsPanels/GeneralPanel.tsx

@@ -1,76 +1,73 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect } from 'react';
 import { useSettingsStore } from '../../../stores/settingsStore';
 import { Toggle } from '../../ui/Toggle';
+import type { InstanceAdminSettings } from '@backspace/shared';
 
 export function GeneralPanel() {
   const instanceSettings = useSettingsStore((s) => s.instanceSettings);
   const updateInstanceSettings = useSettingsStore((s) => s.updateInstanceSettings);
 
-  const [instanceName, setInstanceName] = useState('');
-  const [saveStatus, setSaveStatus] = useState<'idle' | 'saving' | 'saved' | 'error'>('idle');
+  const [draft, setDraft] = useState<InstanceAdminSettings | null>(null);
+  const [saving, setSaving] = useState(false);
   const [saveError, setSaveError] = useState('');
-  const [gifKeyDraft, setGifKeyDraft] = useState('');
+  const [saveSuccess, setSaveSuccess] = useState(false);
   const [gifKeyDirty, setGifKeyDirty] = useState(false);
+  const [gifKeyDraft, setGifKeyDraft] = useState('');
 
   useEffect(() => {
     if (instanceSettings) {
-      setInstanceName(instanceSettings.instanceName);
+      setDraft({ ...instanceSettings });
       setGifKeyDraft('');
       setGifKeyDirty(false);
     }
   }, [instanceSettings]);
 
-  const autoSave = useCallback(async (payload: Record<string, unknown>) => {
-    setSaveStatus('saving');
+  if (!draft) return <div className="text-sm text-txt-tertiary">Loading settings...</div>;
+
+  const baseChanges = instanceSettings && draft
+    ? draft.instanceName !== instanceSettings.instanceName ||
+      draft.registrationOpen !== instanceSettings.registrationOpen ||
+      draft.discoveryEnabled !== instanceSettings.discoveryEnabled
+    : false;
+  const hasChanges = baseChanges || gifKeyDirty;
+
+  const handleSave = async () => {
+    setSaving(true);
     setSaveError('');
+    setSaveSuccess(false);
     try {
+      const payload: Partial<InstanceAdminSettings> = {
+        instanceName: draft!.instanceName,
+        registrationOpen: draft!.registrationOpen,
+        discoveryEnabled: draft!.discoveryEnabled,
+      };
+      if (gifKeyDirty) {
+        payload.gifApiKey = gifKeyDraft;
+      }
       await updateInstanceSettings(payload);
-      setSaveStatus('saved');
-      setTimeout(() => setSaveStatus('idle'), 1500);
-    } catch (err) {
-      setSaveError(err instanceof Error ? err.message : 'Failed to save');
-      setSaveStatus('error');
-      setTimeout(() => { setSaveStatus('idle'); setSaveError(''); }, 3000);
-    }
-  }, [updateInstanceSettings]);
-
-  if (!instanceSettings) return <div className="text-sm text-txt-tertiary">Loading settings...</div>;
-
-  const handleToggle = (key: string, value: boolean) => {
-    autoSave({ [key]: value });
-  };
-
-  const handleInstanceNameBlur = () => {
-    const trimmed = instanceName.trim();
-    if (trimmed && trimmed !== instanceSettings.instanceName) {
-      autoSave({ instanceName: trimmed });
-    }
-  };
-
-  const handleGifKeyBlur = () => {
-    if (gifKeyDirty) {
-      autoSave({ gifApiKey: gifKeyDraft });
       setGifKeyDirty(false);
       setGifKeyDraft('');
+      setSaveSuccess(true);
+      setTimeout(() => setSaveSuccess(false), 2000);
+    } catch (err) {
+      setSaveError(err instanceof Error ? err.message : 'Failed to save');
+    } finally {
+      setSaving(false);
     }
   };
 
-  const handleClearGifKey = () => {
-    autoSave({ gifApiKey: '' });
+  const handleReset = () => {
+    if (instanceSettings) setDraft({ ...instanceSettings });
+    setGifKeyDirty(false);
+    setGifKeyDraft('');
+    setSaveError('');
   };
 
   return (
-    <div className="space-y-5">
-      {/* Save status indicator */}
-      {saveStatus === 'saving' && (
-        <div className="text-xs text-txt-tertiary animate-pulse">Saving...</div>
-      )}
-      {saveStatus === 'saved' && (
-        <div className="text-xs text-status-online">Saved</div>
-      )}
-      {saveStatus === 'error' && (
-        <div className="p-2 bg-accent-rose/10 border border-accent-rose/30 rounded text-txt-danger text-sm">{saveError}</div>
-      )}
+    <form className="space-y-5" onSubmit={(e) => e.preventDefault()}>
+      <div className="text-xs text-txt-tertiary">
+        Configure your Backspace instance. These settings affect all users.
+      </div>
 
       {/* Instance Name */}
       <div>
@@ -79,13 +76,12 @@ export function GeneralPanel() {
         <div className="rounded-lg bg-white/[0.02] p-3.5">
           <input
             type="text"
-            value={instanceName}
-            onChange={(e) => setInstanceName(e.target.value.slice(0, 32))}
-            onBlur={handleInstanceNameBlur}
+            value={draft.instanceName}
+            onChange={(e) => setDraft({ ...draft, instanceName: e.target.value.slice(0, 32) })}
             placeholder="Backspace"
             className="input-standard w-full"
           />
-          <div className="text-[11px] text-txt-tertiary text-right mt-1">{instanceName.length}/32</div>
+          <div className="text-[11px] text-txt-tertiary text-right mt-1">{draft.instanceName.length}/32</div>
         </div>
       </div>
 
@@ -98,7 +94,7 @@ export function GeneralPanel() {
               <div className="text-sm font-medium text-txt-primary">Open Registration</div>
               <div className="text-xs text-txt-tertiary mt-0.5">Allow new users to create accounts on this instance</div>
             </div>
-            <Toggle enabled={instanceSettings.registrationOpen} onChange={(v) => handleToggle('registrationOpen', v)} />
+            <Toggle enabled={draft.registrationOpen} onChange={(v) => setDraft({ ...draft, registrationOpen: v })} />
           </label>
         </div>
       </div>
@@ -112,7 +108,7 @@ export function GeneralPanel() {
               <div className="text-sm font-medium text-txt-primary">Space Discovery</div>
               <div className="text-xs text-txt-tertiary mt-0.5">Allow spaces to appear in the public Explore page</div>
             </div>
-            <Toggle enabled={instanceSettings.discoveryEnabled} onChange={(v) => handleToggle('discoveryEnabled', v)} />
+            <Toggle enabled={draft.discoveryEnabled} onChange={(v) => setDraft({ ...draft, discoveryEnabled: v })} />
           </label>
         </div>
       </div>
@@ -128,20 +124,19 @@ export function GeneralPanel() {
             type="password"
             value={gifKeyDirty ? gifKeyDraft : ''}
             onChange={(e) => { setGifKeyDraft(e.target.value); setGifKeyDirty(true); }}
-            onBlur={handleGifKeyBlur}
-            placeholder={instanceSettings.gifEnabled ? 'Key saved — enter new key to replace' : 'Klipy API key'}
+            placeholder={draft.gifEnabled ? 'Key saved — enter new key to replace' : 'Klipy API key'}
             className="input-standard w-full"
             autoComplete="off"
           />
           <div className="flex items-center gap-2">
             <span className={`inline-flex items-center gap-1 text-[11px] font-medium px-1.5 py-0.5 rounded ${
-              instanceSettings.gifEnabled ? 'bg-status-online/15 text-status-online' : 'bg-white/5 text-txt-tertiary'
+              draft.gifEnabled ? 'bg-status-online/15 text-status-online' : 'bg-white/5 text-txt-tertiary'
             }`}>
-              {instanceSettings.gifEnabled ? 'Enabled' : 'Not configured'}
+              {draft.gifEnabled ? 'Enabled' : 'Not configured'}
             </span>
-            {instanceSettings.gifEnabled && !gifKeyDirty && (
+            {draft.gifEnabled && !gifKeyDirty && (
               <button
-                onClick={handleClearGifKey}
+                onClick={() => { setGifKeyDraft(''); setGifKeyDirty(true); }}
                 className="text-[11px] text-txt-tertiary hover:text-txt-danger transition-colors"
               >
                 Clear key
@@ -150,6 +145,37 @@ export function GeneralPanel() {
           </div>
         </div>
       </div>
-    </div>
+
+      {/* Status messages */}
+      {saveError && (
+        <div className="p-2 bg-accent-rose/10 border border-accent-rose/30 rounded text-txt-danger text-sm">{saveError}</div>
+      )}
+      {saveSuccess && (
+        <div className="p-2 bg-status-online/10 border border-status-online/30 rounded text-status-online text-sm">Settings saved</div>
+      )}
+
+      {/* Save / Reset bar */}
+      {hasChanges && (
+        <div className="sticky bottom-0 z-10 pointer-events-none">
+          <div className="flex justify-center pt-3 pb-1">
+            <div className="glass-bubble rounded-full px-4 py-2 flex items-center gap-2 animate-slide-up pointer-events-auto">
+              <button
+                onClick={handleReset}
+                className="px-3 py-1 text-sm text-txt-tertiary hover:text-txt-secondary transition-colors"
+              >
+                Reset
+              </button>
+              <button
+                onClick={handleSave}
+                disabled={saving}
+                className="px-3 py-1.5 bg-accent-primary hover:bg-accent-primary/80 text-white text-sm font-medium rounded-full transition-colors disabled:opacity-50"
+              >
+                {saving ? 'Saving...' : 'Save'}
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+    </form>
   );
 }