[Enhancement] Native Headless/Server Mode for Remote SSH Development

Problem Description
Currently, using Antigravity Manager in remote development environments (SSH, VS Code Remote, headless Linux servers) is extremely difficult. Because the application is built as a Tauri-based GUI, it fails to launch or hangs indefinitely in headless sessions.

Furthermore, since the proxy and account synchronization logic are tied to the GUI instance, there is no way to manage or switch accounts on a remote server without jumping through hurdles like manual SSH port forwarding or xvfb-run hacks.

Current Behavior

• Application fails to launch/hangs in SSH sessions (no display).
• Proxy binding defaults to 127.0.0.1 and is not exposed for remote CLI tools.
• No CLI-based interface for switching accounts on headless machines.

Expected Behavior
Developers should be able to run a "headless" version of Antigravity Manager on a remote server that provides the same account-switching proxy benefits to remote CLIs (like Claude Code, Gemini CLI, etc.) as the desktop version.

Suggested Enhancements

1. Headless/Server Mode: Add a --headless flag or a separate lightweight binary (e.g., antigravity-server) that runs as a background service without requiring a GUI environment (X11/Wayland).
2. Remote Management CLI: Provide a simple CLI tool (e.g., ag-switch) that can interact with the running server to switch active accounts/profiles via the terminal.
3. Configurable Bind Address: Allow the manager to bind its proxy to specific interfaces (not just 127.0.0.1) to facilitate remote access in secure environments.
4. Remote Agent Decoupling: Ensure the "Agent" logic can load independently of the React-Tauri lifecycle to prevent freezes in terminal-only environments.

Workarounds Tried

• xvfb-run (unstable and resource-heavy for a background manager).
• Manual SSH Tunneling (tedious to maintain for multiple tool ports).