feat(FRE-596): add PWA setup and responsive design

- Register service worker for offline caching (app shell + API responses)
- Link manifest.json in index.html with updated theme colors
- Update manifest start_url to /app/dashboard for PWA experience
- Add comprehensive team management CSS with responsive breakpoints
- Add alert, loading, and danger button styles
- Mobile-first responsive layout for team list and detail views

public/manifest.json

@@ -1,21 +1,27 @@
 {
-  "name": "Scripter",
+  "name": "Scripter — Write Faster",
   "short_name": "Scripter",
   "description": "Professional screenplay editor with real-time collaboration",
-  "start_url": "/",
+  "start_url": "/app/dashboard",
   "display": "standalone",
-  "background_color": "#1a1a2e",
-  "theme_color": "#1a1a2e",
+  "background_color": "#0a0a0a",
+  "theme_color": "#0a0a0a",
   "orientation": "any",
   "icons": [
     {
-      "src": "/icon-192.png",
+      "src": "/src-tauri/128x128.png",
+      "sizes": "128x128",
+      "type": "image/png",
+      "purpose": "any maskable"
+    },
+    {
+      "src": "/src-tauri/128x128.png",
       "sizes": "192x192",
       "type": "image/png",
       "purpose": "any maskable"
     },
     {
-      "src": "/icon-512.png",
+      "src": "/src-tauri/128x128.png",
       "sizes": "512x512",
       "type": "image/png",
       "purpose": "any maskable"