feat: production hardening

[aeswibon]

Description

Implement production hardening features including namespace-scoped security, advanced resource health assessment (Deployment/Pod status), SOPS idempotency hardening, and expanded Prometheus metrics.

Fixes #31

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation update

How Has This Been Tested?

• Unit tests for controller health checks and sync logic (coverage increased to 80.5%)
• Integration tests for k8s client-set and SOPS decryption
• Manual verification via TUI dashboard

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Local pre-commit checks pass successfully