v0.5.2-beta: Add System Status endpoint and UI (operational checks)

[DeepZone]

Motivation

• Provide operators with an operational overview of a running RouteForge installation including DB health, RIPEstat runtime settings and active features.
• Surface read-only safety, demo/live mode and API-proxy visibility without adding new routing domain functionality or write capabilities.
• Keep existing endpoints and UX stable while improving observability for self-hosted deployments.

Description

• Added backend/app/core/system_status.py implementing build_system_status, get_database_status and safe_database_url to mask secrets and derive DB type, and perform a SELECT 1 when an engine is available.
• Added GET /api/system/status in backend/app/api/routes_system.py while keeping /api/system/info compatible and extended /health non-breakingly to include version and database status.
• Frontend changes include getSystemStatus() in frontend/src/api.ts, new defensive types in frontend/src/types.ts, a new "System" navigation entry and System view in frontend/src/App.tsx/frontend/src/components/Layout.tsx, and a small System card on the Dashboard.
• Documentation and packaging updated: README.md, RELEASE_NOTES.md, docs/operations/system-status.md, and version bumps to user-facing v0.5.2-beta and package/runtime 0.5.2.
• Tests: backend smoke tests extended (backend/tests/test_api_smoke.py) with test_system_status_endpoint and test_safe_database_url and code organized so routes remain readable.

Testing

• Ran backend tests with cd backend && pytest -q, which completed successfully (75 passed).
• Verified frontend production build with cd frontend && npm run build, which completed successfully.
• Confirmed the health and system endpoints return the expected shape and that no secrets are exposed by safe_database_url during tests.

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Codex Task