fix: bump SW version and switch to network-first caching

VERSION was stuck at raycer-v1 so mobile PWAs never picked up
the streak fix (cache-first served the stale stats.js forever).

- Bump to raycer-v2 → triggers install, purges old caches
- Switch same-origin assets from cache-first to network-first
  so future deploys propagate immediately; cache is only used
  as an offline fallback
- Simplify to a single SHELL_CACHE (no separate runtime cache)
- Cross-origin vendor assets (Dexie CDN) stay cache-first

frontend/public/sw.js

@@ -1,14 +1,13 @@
 /* raycer service worker
- * - app shell: cache-first
+ * - app shell: network-first (so deploys propagate immediately), cache fallback for offline
- * - /api/*: network-first with no cache fallback (data lives in Dexie)
+ * - /api/*: network-only (data lives in Dexie)
- * - dexie CDN module: cache-first (so the app boots offline)
+ * - cross-origin (Dexie CDN): cache-first (immutable vendor assets)
  */
 
-const VERSION = 'raycer-v1';
+const VERSION = 'raycer-v2';
 const SHELL_CACHE = `${VERSION}-shell`;
-const RUNTIME_CACHE = `${VERSION}-runtime`;
 
-const SHELL = [
+const PRECACHE = [
   '/',
   '/index.html',
   '/manifest.webmanifest',
@@ -28,7 +27,7 @@ self.addEventListener('install', (event) => {
   event.waitUntil(
     (async () => {
       const cache = await caches.open(SHELL_CACHE);
-      await cache.addAll(SHELL);
+      await cache.addAll(PRECACHE);
       self.skipWaiting();
     })()
   );
@@ -40,7 +39,7 @@ self.addEventListener('activate', (event) => {
       const keys = await caches.keys();
       await Promise.all(
         keys
-          .filter((k) => !k.startsWith(VERSION))
+          .filter((k) => k !== SHELL_CACHE)
           .map((k) => caches.delete(k))
       );
       await self.clients.claim();
@@ -54,7 +53,7 @@ self.addEventListener('fetch', (event) => {
 
   const url = new URL(req.url);
 
-  // API: network-first, never cache
+  // API: network-only, never cache
   if (url.pathname.startsWith('/api/')) {
     event.respondWith(
       fetch(req).catch(
@@ -67,39 +66,24 @@ self.addEventListener('fetch', (event) => {
     return;
   }
 
-  // Same-origin SPA navigations: serve cached shell, fall back to network
+  // Same-origin (app shell + assets): network-first, cache fallback for offline
-  if (req.mode === 'navigate') {
-    event.respondWith(
-      (async () => {
-        try {
-          const fresh = await fetch(req);
-          const cache = await caches.open(SHELL_CACHE);
-          cache.put('/index.html', fresh.clone()).catch(() => {});
-          return fresh;
-        } catch {
-          const cached = await caches.match('/index.html');
-          if (cached) return cached;
-          return new Response('offline', { status: 503 });
-        }
-      })()
-    );
-    return;
-  }
-
-  // Same-origin assets: cache-first
   if (url.origin === self.location.origin) {
     event.respondWith(
       (async () => {
-        const cached = await caches.match(req);
-        if (cached) return cached;
         try {
           const fresh = await fetch(req);
           if (fresh.ok) {
-            const cache = await caches.open(RUNTIME_CACHE);
+            const cache = await caches.open(SHELL_CACHE);
             cache.put(req, fresh.clone()).catch(() => {});
           }
           return fresh;
         } catch {
+          const cached = await caches.match(req);
+          if (cached) return cached;
+          if (req.mode === 'navigate') {
+            const shell = await caches.match('/index.html');
+            if (shell) return shell;
+          }
           return new Response('offline', { status: 503 });
         }
       })()
@@ -107,7 +91,7 @@ self.addEventListener('fetch', (event) => {
     return;
   }
 
-  // Cross-origin (e.g. Dexie CDN): cache-first
+  // Cross-origin (e.g. Dexie CDN): cache-first (immutable vendor assets)
   event.respondWith(
     (async () => {
       const cached = await caches.match(req);
@@ -115,12 +99,12 @@ self.addEventListener('fetch', (event) => {
       try {
         const fresh = await fetch(req);
         if (fresh.ok) {
-          const cache = await caches.open(RUNTIME_CACHE);
+          const cache = await caches.open(SHELL_CACHE);
           cache.put(req, fresh.clone()).catch(() => {});
         }
         return fresh;
       } catch {
-        return cached || new Response('offline', { status: 503 });
+        return new Response('offline', { status: 503 });
       }
     })()
   );