feat: PWA install prompt, brand-colored channel icons, image load fix, semantic connection indicator

- Fix image display bug: remove loading='lazy' + use opacity instead of hidden (#66)
- PWA: add id/scope to manifest, fix SW cache name, add install prompt hook + button (#64)
- Colorize channel icons with brand colors (Discord blurple, Telegram blue, etc.) (#68)
- Use semantic green for connection indicator instead of theme accent (#70)
- Replace Sparkles icon with PinchChat logo in sidebar (#65)
- Replace decorative dots in sidebar footer with GitHub link (#71)

public/manifest.json

@@ -1,8 +1,10 @@
 {
+  "id": "/",
   "name": "PinchChat",
   "short_name": "PinchChat",
   "description": "A sleek, dark-themed webchat UI for OpenClaw — monitor sessions, stream responses, and inspect tool calls in real-time.",
   "start_url": "/",
+  "scope": "/",
   "display": "standalone",
   "background_color": "#1e1e24",
   "theme_color": "#1e1e24",

public/sw.js

@@ -1,5 +1,5 @@
 // PinchChat Service Worker — cache static assets for offline/instant load
-const CACHE_NAME = 'pinchchat-__SW_VERSION__';
+const CACHE_NAME = 'pinchchat-v1';
 
 // Cache static assets on install
 self.addEventListener('install', (event) => {