feat(plugins): enforce sandbox isolation for third-party plugins

[SurviveM]

Requirements

Third-party plugins must run in an isolated child process with no access to main process memory. A malicious plugin with process.exit() should not crash the host. Plugin crashes must not affect main process stability.

Verification

1. Write a test plugin that calls process.exit(1) on load
2. Load the plugin and trigger its execution
3. Verify main process stays alive (no crash, no uncaught exception)
4. Verify plugin failure is logged and the plugin is marked as failed
5. After recovery, verify the plugin can be reloaded and executed normally