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

requirements.txt

@@ -0,0 +1,6 @@
+# Sidecar V2 — Multi-Pool Provider Proxy
+fastapi>=0.115.0,<1.0.0
+uvicorn[standard]>=0.30.0,<1.0.0
+httpx>=0.27.0,<1.0.0
+structlog>=24.0.0,<25.0.0
+cryptography>=42.0.0,<44.0.0