feat: v2 React frontend is now primary at /

- v1 vanilla JS frontend moved to /classic (static/classic/)
- v2 React app now serves at / (root)
- Vite base changed from /v2/ to /
- Assets at /assets/, service worker at /sw.js
- /classic still works — all v1 files preserved with relative paths
- /v2 still works as before (build output unchanged)

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

static/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;
+  }
+});