feat: Sidecar V2 — multi-pool provider proxy with 429 cooldown

- proxy.py: Fix route path duplication (v1/v1 → v1) when upstream
  base URL already includes /v1 prefix
- proxy.py: Fix _emergency_count global variable for metrics tracking
- server.py: Add logging.basicConfig(level=logging.INFO) for structlog
  INFO-level log visibility
- Full multi-pool routing: primary → fallback → emergency passthrough
- Per-backend rate limiting with RPM-based token bucket
- 429 cooldown mechanism with automatic recovery
- Dashboard with SSE real-time monitoring
- Admin API for backend/pool/config management
- SQLite-backed persistence with encrypted API key storage
- Docker compose deployment

Deployed by opengineer 严维序 as BIZ-50 Step 4

.gitignore

@@ -0,0 +1,20 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+venv/
+
+# Environment
+.env
+
+# Data
+data/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS
+.DS_Store