feat: add frontend Rich Presence — activityStore, ActivityCard, sidebar upgrades, settings toggle

- Task 7: Create activityStore (Zustand) with Map<userId, Activity[]>, showActivity toggle,
  debounced pushActivities, and reset on logout
- Task 8: Wire WS integration — presence_update propagates activities to store,
  ready payload initializes userActivities and showActivity (via setState to avoid side effects)
- Task 9: Create ActivityCard component with compact/full modes, type-colored labels,
  elapsed time display, asset images, and fallback to customStatus
- Task 10: Upgrade ActivityPanel to three groups — active friends (full cards, no header),
  online friends (compact), offline friends — using getPrimaryActivity for grouping
- Task 11: Upgrade MemberSidebar to show compact ActivityCards instead of raw customStatus
- Task 12: Add showActivity toggle in AccountPanel settings (Activity Status section)
  with API persistence and store sync

packages/web/src/components/modals/settingsPanels/AccountPanel.tsx

@@ -11,6 +11,7 @@ import type { User, UserStatus, AvatarColor } from '@backspace/shared';
 import type { FederationOpResult } from '../../../utils/federationOps';
 import { isElectron } from '../../../platform/platform';
 import { Toggle } from '../../ui/Toggle';
+import { useActivityStore } from '../../../stores/activityStore';
 
 
 function AutoLaunchSettings() {
@@ -139,6 +140,7 @@ export function AccountPanel() {
 
   const instances = useInstanceStore((s) => s.instances);
   const changePassword = useAuthStore((s) => s.changePassword);
+  const showActivity = useActivityStore((s) => s.showActivity);
 
   if (!user) return null;
 
@@ -775,6 +777,30 @@ export function AccountPanel() {
         </div>
       )}
 
+      {/* ── Activity Status ── */}
+      <div>
+        <div className="text-[11px] font-semibold text-txt-tertiary uppercase tracking-wider mb-1.5">Activity Status</div>
+        <div className="rounded-lg bg-white/[0.03] border border-white/[0.04] p-3.5">
+          <div className="flex items-center justify-between py-1">
+            <div>
+              <div className="text-[14px] text-txt-primary">Share Activity Status</div>
+              <div className="text-[12px] text-txt-tertiary mt-0.5">Allow others to see what you're up to</div>
+            </div>
+            <Toggle
+              enabled={showActivity}
+              onChange={async (enabled) => {
+                try {
+                  await api.users.update({ showActivity: enabled });
+                  useActivityStore.getState().setShowActivity(enabled);
+                } catch (err) {
+                  console.error('Failed to update activity visibility:', err);
+                }
+              }}
+            />
+          </div>
+        </div>
+      </div>
+
       {/* ── Danger Zone ── */}
       <div>
         <div className="text-[11px] font-semibold text-txt-tertiary uppercase tracking-wider mb-1.5">Danger Zone</div>