Add PWA support for install-to-home-screen

Adds manifest.json, service worker with static asset caching,
resized cat icons, and meta tags for iOS/Android installability.

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

raggr-frontend/public/manifest.json

@@ -0,0 +1,14 @@
+{
+  "name": "Ask Simba",
+  "short_name": "Simba",
+  "description": "Chat with Simba - your AI cat companion",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#FAF8F2",
+  "theme_color": "#2A4D38",
+  "icons": [
+    { "src": "/pwa-icon-192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/pwa-icon-512.png", "sizes": "512x512", "type": "image/png" },
+    { "src": "/pwa-icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
+  ]
+}

raggr-frontend/public/sw.js

@@ -0,0 +1,46 @@
+const CACHE = 'simba-v1';
+
+self.addEventListener('install', (e) => {
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', (e) => {
+  e.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k)))
+    )
+  );
+  self.clients.claim();
+});
+
+self.addEventListener('fetch', (e) => {
+  const { request } = e;
+  const url = new URL(request.url);
+
+  // Network-only for API calls
+  if (url.pathname.startsWith('/api/')) return;
+
+  // Cache-first for fingerprinted static assets
+  if (url.pathname.startsWith('/static/')) {
+    e.respondWith(
+      caches.match(request).then(
+        (cached) =>
+          cached ||
+          fetch(request).then((res) => {
+            const clone = res.clone();
+            caches.open(CACHE).then((c) => c.put(request, clone));
+            return res;
+          })
+      )
+    );
+    return;
+  }
+
+  // Network-first for navigation (offline fallback to cache)
+  if (request.mode === 'navigate') {
+    e.respondWith(
+      fetch(request).catch(() => caches.match(request))
+    );
+    return;
+  }
+});