feat: implement Phase 2 Civitai Guard (v0.2)

[MrBT-nano]

📝 Description

This PR implements Phase 2 (v0.2) of the project: Civitai Guard and Allowlist Enforcement.

Key changes:

• Rust Allowlist Watcher: Implemented a thread-safe in-memory cache and file watcher to synchronize authorized models from vtuber-commons.
• gRPC Enforcement: Updated the Generate method to verify persona/model configurations against the allowlist before processing.
• Python Runtime Verification: Added SHA256 hash and NSFW status validation against the Civitai API in the worker.
• Infrastructure: Added Kubernetes Deployment manifest with git-sync sidecar for config synchronization.

🛠️ Type of Change

• 🚀 New feature

✅ Checklist

• Rust build (cargo build) passes
• Python unit tests pass (5/5 tests)
• STRUCTURE.tree updated
• K8s manifests provided

🏷️ Metadata

• Assignee: @MrBT-nano
• Labels: enhancement