feat(sandbox): implement cross-platform support with Windows fallback

- Add conditional compilation for Unix-specific gaol sandbox functionality
- Implement Windows-compatible SandboxExecutor with no-op sandboxing
- Update ProfileBuilder to handle both Unix and Windows platforms
- Add platform-specific dependency declaration for gaol crate
- Modify agent and claude commands to use appropriate sandbox implementation
- Update test modules with conditional compilation for Unix-only tests
- Ensure graceful degradation on Windows with logging warnings

This change enables the application to build and run on Windows while
maintaining full sandbox security on Unix-like systems.

src-tauri/Cargo.toml

@@ -50,6 +50,9 @@ zstd = "0.13"
 uuid = { version = "1.6", features = ["v4", "serde"] }
 walkdir = "2"
 
+[target.'cfg(unix)'.dependencies]
+gaol = "0.2"
+
 [target.'cfg(target_os = "macos")'.dependencies]
 cocoa = "0.26"
 objc = "0.2"