feat: agent brain (ollama) and chat ui

.living_spec/specs/tech/STACK.md

@@ -78,6 +78,8 @@ To support both Remote and Local models, the system implements a `ModelProvider`
     *   `walkdir`: Simple directory traversal.
     *   `tokio`: Async runtime.
     *   `reqwest`: For LLM API calls (if backend-initiated).
+    *   `uuid`: For unique message IDs.
+    *   `chrono`: For timestamps.
     *   `tauri-plugin-dialog`: Native system dialogs.
 *   **JavaScript:**
     *   `@tauri-apps/api`: Tauri Bridge.