refactor: unify settings into tabbed modal with UI polish

Split monolithic UserSettings into AccountPanel, VoicePanel, ConnectionsPanel,
and InstancePanel tabs. Remove standalone InstanceSettings modal. Add reusable
Toggle component fixing size deformation, color inconsistency (green→purple),
and flex-shrink issues. Fix custom status clearing by always sending the field
to the server. Wrap Log Out button in glass bubble. Add subtle card depth with
borders.

packages/web/src/stores/authStore.ts

@@ -1,5 +1,5 @@
 import { create } from 'zustand';
-import type { User } from '@backspace/shared';
+import type { User, UserStatus } from '@backspace/shared';
 import { api } from '../api/client';
 import { useChatStore } from './chatStore';
 import { useSpaceStore } from './spaceStore';
@@ -16,7 +16,7 @@ interface AuthState {
   register: (username: string, password: string, displayName?: string) => Promise<void>;
   logout: () => void;
   loadUser: () => Promise<void>;
-  updateProfile: (data: { displayName?: string; avatar?: string; customStatus?: string }) => Promise<void>;
+  updateProfile: (data: { displayName?: string; avatar?: string; customStatus?: string; status?: UserStatus }) => Promise<void>;
   setUser: (user: User) => void;
   clearError: () => void;
 }

packages/web/src/stores/uiStore.ts

@@ -10,7 +10,6 @@ type ModalType =
   | 'userSettings'
   | 'spaceSettings'
   | 'channelSettings'
-  | 'instanceSettings'
   | 'imagePreview'
   | 'newDm'
   | 'addDmMember'