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/layout/MemberSidebar.tsx

@@ -2,8 +2,10 @@ import React, { useMemo } from 'react';
 import type { MemberWithUser } from '@backspace/shared';
 import { useSpaceStore } from '../../stores/spaceStore';
 import { useUIStore } from '../../stores/uiStore';
+import { useActivityStore } from '../../stores/activityStore';
 import { Avatar } from '../ui/Avatar';
 import { Username } from '../ui/Username';
+import { ActivityCard } from '../ui/ActivityCard';
 import { parseFederatedUsername } from '../../utils/identity';
 
 /**
@@ -47,6 +49,7 @@ export function MemberSidebar() {
   const currentSpaceId = useSpaceStore((s) => s.currentSpaceId);
   const memberListOpen = useUIStore((s) => s.memberListOpen);
   const openUserProfile = useUIStore((s) => s.openUserProfile);
+  const userActivities = useActivityStore((s) => s.userActivities);
 
   const space = spaces.find(s => s.id === currentSpaceId);
   const ownerId = space?.ownerId;
@@ -122,8 +125,12 @@ export function MemberSidebar() {
           {domain && !isOffline && (
             <div className="text-[10px] leading-[1.3] text-txt-tertiary truncate opacity-60">@{domain}</div>
           )}
-          {!isOffline && member.user.customStatus && (
-            <div className="text-[11px] leading-[1.3] text-txt-tertiary truncate">{member.user.customStatus}</div>
+          {!isOffline && (
+            <ActivityCard
+              activities={userActivities.get(member.userId) ?? []}
+              compact={true}
+              fallbackCustomStatus={member.user.customStatus}
+            />
           )}
         </div>
       </div>