Match desktop chat layout with web version

- Change agent icon from Headphones to MessageCircle
- Adjust avatar size to size-7 and icons to size-3.5
- Reposition attach button next to send button (textarea -> attach -> send)
- Add Online indicator in header with animated green dot
- Implement minimized state (collapsed view like web)
- Hide web chat widget when running in Tauri context (avoid duplicate)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/chat/chat-widget.tsx

@@ -231,6 +231,10 @@ function MessageAttachment({ attachment }: { attachment: ChatAttachment }) {
 }
 
 export function ChatWidget() {
+  // Detectar se esta rodando no Tauri (desktop) - nesse caso, nao renderizar
+  // pois o chat nativo do Tauri ja esta disponivel
+  const isTauriContext = typeof window !== "undefined" && "__TAURI__" in window
+
   const { convexUserId } = useAuth()
   const viewerId = convexUserId ?? null
 
@@ -460,7 +464,10 @@ export function ChatWidget() {
     }
   }
 
-  // Não mostrar se não logado ou sem sessões
+  // Nao mostrar se esta no Tauri (usa o chat nativo)
+  if (isTauriContext) return null
+
+  // Nao mostrar se nao logado ou sem sessoes
   if (!viewerId) return null
   if (!activeSessions || activeSessions.length === 0) return null