Polish chat UI and wire flue agent env

- Add chat components (header, composer, conversation, message, thinking response, identity)
- Add chat hooks (use-chat-agent, use-chat-composer)
- Add chat lib (constants, transforms, types)
- Wire agent model config through env (provider, name, api, base url, key, context window, max tokens)
- Refresh web styling and routes

.env.example

@@ -8,6 +8,8 @@ NATIVE_APP_URL=code://
 # Browser and native public endpoints
 VITE_CONVEX_URL=https://example.convex.cloud
 VITE_CONVEX_SITE_URL=https://example.convex.site
+# For phone testing, replace localhost with this machine's Tailscale IPv4 address.
+VITE_FLUE_URL=http://localhost:3583
 EXPO_PUBLIC_CONVEX_URL=https://example.convex.cloud
 EXPO_PUBLIC_CONVEX_SITE_URL=https://example.convex.site