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

storage/config_store.py

@@ -0,0 +1,55 @@
+"""System configuration KV store operations."""
+
+import time
+from typing import Optional, Any
+
+from storage.db import get_connection
+
+
+def get_config(key: str) -> Optional[str]:
+    """Get a single config value."""
+    with get_connection() as conn:
+        row = conn.execute(
+            "SELECT value FROM system_config WHERE key = ?", (key,)
+        ).fetchone()
+    return row["value"] if row else None
+
+
+def set_config(key: str, value: str, description: str = "") -> None:
+    """Set or update a config value."""
+    now = time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())
+    with get_connection() as conn:
+        conn.execute(
+            """INSERT INTO system_config (key, value, description, updated_at)
+               VALUES (?, ?, ?, ?)
+               ON CONFLICT(key) DO UPDATE SET
+               value = excluded.value,
+               description = excluded.description,
+               updated_at = excluded.updated_at""",
+            (key, value, description, now),
+        )
+        conn.commit()
+
+
+def delete_config(key: str) -> bool:
+    """Delete a config value."""
+    with get_connection() as conn:
+        cursor = conn.execute(
+            "DELETE FROM system_config WHERE key = ?", (key,)
+        )
+        conn.commit()
+        return cursor.rowcount > 0
+
+
+def list_configs() -> list[dict]:
+    """List all system config entries."""
+    with get_connection() as conn:
+        rows = conn.execute("SELECT * FROM system_config ORDER BY key").fetchall()
+    return [dict(row) for row in rows]
+
+
+def get_all_configs_as_dict() -> dict[str, str]:
+    """Get all configs as a simple dict."""
+    with get_connection() as conn:
+        rows = conn.execute("SELECT key, value FROM system_config").fetchall()
+    return {row["key"]: row["value"] for row in rows}