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/public/sw.js

@@ -0,0 +1,72 @@
+// Service worker for MosswartOverlord v2 — caches static assets for instant repeat loads
+const CACHE_NAME = 'mo-v2-cache-v1';
+const STATIC_ASSETS = [
+  '/dereth.png',
+  '/dereth_highres.png',
+  '/prismatic-taper-icon.png',
+  '/icons/0600127E.png',
+  '/icons/06000133.png',
+  '/icons/06001080.png',
+];
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then(cache => cache.addAll(STATIC_ASSETS))
+  );
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then(keys =>
+      Promise.all(keys.filter(k => k !== CACHE_NAME).map(k => caches.delete(k)))
+    )
+  );
+  self.clients.claim();
+});
+
+self.addEventListener('fetch', (event) => {
+  const url = new URL(event.request.url);
+
+  // Cache icon images on first fetch
+  if (url.pathname.startsWith('/icons/') && event.request.method === 'GET') {
+    event.respondWith(
+      caches.match(event.request).then(cached => {
+        if (cached) return cached;
+        return fetch(event.request).then(response => {
+          if (response.ok) {
+            const clone = response.clone();
+            caches.open(CACHE_NAME).then(cache => cache.put(event.request, clone));
+          }
+          return response;
+        });
+      })
+    );
+    return;
+  }
+
+  // Cache dungeon_tiles.json (large, rarely changes)
+  if (url.pathname === '/dungeon_tiles.json') {
+    event.respondWith(
+      caches.match(event.request).then(cached => {
+        if (cached) return cached;
+        return fetch(event.request).then(response => {
+          if (response.ok) {
+            const clone = response.clone();
+            caches.open(CACHE_NAME).then(cache => cache.put(event.request, clone));
+          }
+          return response;
+        });
+      })
+    );
+    return;
+  }
+
+  // Cache static assets (map images etc)
+  if (STATIC_ASSETS.some(a => url.pathname === a)) {
+    event.respondWith(
+      caches.match(event.request).then(cached => cached || fetch(event.request))
+    );
+    return;
+  }
+});