feat: refactor ACP, add prompt attachments, auto-approve permissions and optimize streaming

- ACP Attachments: Added support for sending prompt attachments (images, audio, and text files).
  - Frontend: Integrated drag-and-drop, paste-to-upload, file selector, and microphone audio recording (using MediaRecorder) in AcpInput.
  - Backend: Added automatic file path detection in prompt texts to load local workspace files. Created a secure endpoint `/api/local-image` to serve workspace images.
- Automated Permissions: Removed manual agent permission prompts. All permission requests are now automatically approved on the backend. Removed permission UI components and handlers.
- Stream Optimization: Implemented a 100ms message flush buffer on the frontend to throttle state updates during rapid token streaming, preventing UI lagging.
- Proxy and Cleanup: Configured Vite API proxying to direct `/api` routes to the backend. Cleaned up unused helper functions in Cargo config, utilities, history, and app state.

Author: vipmax

anycode-backend/Cargo.lock

@@ -53,3 +53,4 @@ async-trait = "0.1"
 tokio-util = { version = "0.7.13", features = ["compat"] }
 unicode-segmentation = "1.12.0"
 git2 = "0.20"
+base64 = "0.22"