feat: system service management (gyandoot service install|remove|status)

- Create systemd + launchd service templates in resources/
- Add gyandoot-core/src/service.rs module with full lifecycle
  - systemd: user service, daemon-reload, enable, start, stop, disable
  - launchd: macOS plist, load/unload, start/stop (launchctl)
- Add 'gyandoot service install|remove|status' CLI subcommand
- Update setup wizard: prompts 'Install system service? [y/N]'
- Update install.sh: prompts user for service install after binary
- Browser auto-starts at runtime (browser_manager), no separate service needed
- Camoufox installed via npm, auto-started by GyanDoot agent loop

crates/gyandoot-core/src/lib.rs

@@ -7,6 +7,7 @@
 pub mod types;
 pub mod config;
 pub mod error;
+pub mod service;
 
 pub use types::*;
 pub use config::*;