[codex] Implement vhost detail page

[bihius]

Summary

• Replace the VHost detail placeholder with a real metadata, policy assignment, and rule override view.
• Add frontend API and type contracts for VHost detail and rule override CRUD.
• Add focused tests for loading, permissions, policy reassignment, and override management.

Closes #198

Validation

• pnpm run type-check
• pnpm run lint
• pnpm test