perf(v2): 8 optimizations — 24% smaller bundle, fewer re-renders

1. React.memo on WindowRenderer — prevents re-renders when parent
   state changes but no windows are affected

2. Coordinate display via direct DOM ref — no React state updates
   on mouse move (was triggering re-renders on every pixel)

3. useDeferredValue for sidebar vitals + player list — React
   prioritizes map interactions over stat text updates

4. Chat messages in ref — stores in useRef instead of useState,
   only bumps a version counter for re-render. Eliminates a
   new Map() allocation on every chat message.

5. Lazy-load 8 window components — InventoryWindow, CharacterWindow,
   RadarWindow, CombatStatsWindow, IssuesWindow, VitalSharingWindow,
   StatsWindow, CombatPickerWindow all loaded on first open.
   Main bundle dropped from 278KB to 211KB (24% reduction).

6. Preload critical assets — dereth.png, backpack icon, dungeon_tiles.json
   via <link rel="preload"> in index.html for instant map render.

7. Bundle splitting — React runtime extracted to separate 12KB chunk
   (cached independently). Window components split into 8 chunks.
   Total: 13 chunks vs previous 2.

8. Service worker — caches map images, icon sprites, and dungeon tiles.
   Icon images cached on first fetch. Repeat page loads serve from
   cache instantly. Auto-cleans old cache versions.

Net result:
- Initial load: 211KB main + 17KB CSS (was 278KB + 17KB)
- React cached separately: 12KB
- Windows load on demand: 1-15KB each
- Dashboard with Recharts: 425KB (unchanged, still lazy)
- Map images/icons: cached by service worker after first load

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/map/Sidebar.tsx

@@ -33,8 +33,9 @@ export const Sidebar: React.FC<Props> = ({
 
   const isOnline = serverHealth?.status?.toLowerCase() === 'online' || serverHealth?.status?.toLowerCase() === 'up';
 
-  // Defer player list rendering — kill counters don't need 30fps updates
+  // Defer player list rendering — sidebar stats don't need real-time updates
   const deferredPlayers = useDeferredValue(players);
+  const deferredVitals = useDeferredValue(vitals);
 
   const sorted = useMemo(() => {
     let list = [...deferredPlayers];
@@ -110,7 +111,7 @@ export const Sidebar: React.FC<Props> = ({
 
       <PlayerList
         players={sorted}
-        vitals={vitals}
+        vitals={deferredVitals}
         getColor={getColor}
         onSelect={onSelectPlayer}
       />