feat: Discord-style presence status selector

Adds a manual presence picker to the sidebar user avatar. Clicking the
avatar opens a popout menu with Online, Idle, Do Not Disturb, Invisible,
and Auto (activity-based) options. The selected status is shown as a
colored badge on the avatar and stored in settings (survives reloads).

usePresenceUpdater now short-circuits for manual states and only runs
the full activity-tracking logic in Auto mode.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/state/settings.ts

@@ -45,6 +45,7 @@ export interface Settings {
   pageZoom: number;
   hideActivity: boolean;
   hidePresence: boolean;
+  presenceStatus: 'auto' | 'online' | 'idle' | 'dnd' | 'invisible';
 
   isPeopleDrawer: boolean;
   memberSortFilterIndex: number;
@@ -89,6 +90,7 @@ const defaultSettings: Settings = {
   pageZoom: 100,
   hideActivity: false,
   hidePresence: false,
+  presenceStatus: 'auto',
 
   isPeopleDrawer: true,
   memberSortFilterIndex: 0,