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

config.py

@@ -0,0 +1,165 @@
+"""System configuration management for Sidecar V2."""
+
+import os
+import json
+from dataclasses import dataclass, field, asdict
+from typing import Optional
+
+
+@dataclass
+class Config:
+    """Sidecar V2 runtime configuration.
+
+    Sources (priority order):
+    1. Environment variables (highest)
+    2. system_config table in SQLite
+    3. Defaults defined here
+    """
+
+    # Listen
+    host: str = "127.0.0.1"
+    port: int = 9190
+    metrics_port: int = 9191
+
+    # Queue
+    queue_max_depth: int = 500
+    queue_timeout_seconds: float = 30.0
+
+    # Provider
+    default_rpm_limit: int = 40
+
+    # Cooldown
+    cooldown_base_seconds: float = 30.0
+    cooldown_max_seconds: float = 600.0
+    cooldown_exponential_backoff: bool = True
+
+    # Emergency channel: RPM fraction when all pools exhausted
+    emergency_rpm_fraction: float = 0.10
+
+    # Health check
+    health_check_interval_seconds: int = 60
+    health_check_timeout_seconds: int = 10
+    health_probe_endpoint: str = "/v1/models"
+
+    # Admin auth
+    admin_token: str = ""
+
+    # Encryption
+    encryption_key: str = ""
+
+    # Logging
+    log_level: str = "INFO"
+
+    # Database
+    db_path: str = ""
+    backup_dir: str = ""
+    backup_retention_days: int = 7
+
+    # Rate limiter
+    rate_limiter_refill_interval_ms: int = 50
+
+    # Router
+    router_refresh_interval_seconds: float = 5.0
+
+    # Max pool-internal retries
+    max_pool_retries: int = 5
+
+    # Pre-check cooldown threshold (seconds remaining)
+    cooldown_precheck_threshold_seconds: float = 10.0
+
+    # Dashboard
+    dashboard_sse_interval_seconds: float = 1.0
+
+    # Stats
+    stats_refresh_interval_seconds: float = 30.0
+
+    # Request timeout
+    default_request_timeout_seconds: int = 120
+
+    @classmethod
+    def from_env(cls) -> "Config":
+        """Load configuration from environment variables."""
+        c = cls()
+
+        # Listen
+        c.host = os.getenv("SIDECAR_HOST", c.host)
+        c.port = int(os.getenv("SIDECAR_PORT", str(c.port)))
+        c.metrics_port = int(os.getenv("SIDECAR_METRICS_PORT", str(c.metrics_port)))
+
+        # Queue
+        c.queue_max_depth = int(os.getenv("SIDECAR_QUEUE_MAX", str(c.queue_max_depth)))
+        c.queue_timeout_seconds = float(
+            os.getenv("SIDECAR_QUEUE_TIMEOUT", str(c.queue_timeout_seconds))
+        )
+
+        # Provider
+        c.default_rpm_limit = int(
+            os.getenv("SIDECAR_RATE_RPM", str(c.default_rpm_limit))
+        )
+
+        # Cooldown
+        c.cooldown_base_seconds = float(
+            os.getenv("SIDECAR_COOLDOWN_BASE", str(c.cooldown_base_seconds))
+        )
+        c.cooldown_max_seconds = float(
+            os.getenv("SIDECAR_COOLDOWN_MAX", str(c.cooldown_max_seconds))
+        )
+
+        # Admin
+        c.admin_token = os.getenv("SIDECAR_ADMIN_TOKEN", c.admin_token)
+
+        # Encryption
+        c.encryption_key = os.getenv("SIDECAR_ENCRYPTION_KEY", c.encryption_key)
+
+        # Logging
+        c.log_level = os.getenv("LOG_LEVEL", c.log_level).upper()
+
+        # Database
+        c.db_path = os.getenv(
+            "SIDECAR_DB_PATH",
+            os.path.join(os.getcwd(), "data", "sidecar_v2.db"),
+        )
+        c.backup_dir = os.getenv(
+            "SIDECAR_BACKUP_DIR",
+            os.path.join(os.getcwd(), "data", "backups"),
+        )
+
+        # V1 compatibility: migrate env vars
+        c._migrate_v1_env()
+
+        return c
+
+    def _migrate_v1_env(self) -> None:
+        """Migrate V1 environment variables to V2 defaults."""
+        # V1 UPSTREAM endpoint
+        upstream = os.getenv("SIDECAR_UPSTREAM")
+        api_key = os.getenv("SIDECAR_API_KEY")
+        if api_key and self.encryption_key:
+            # These will be used during initial migration
+            os.environ["_SIDECAR_V1_API_KEY"] = api_key
+            os.environ["_SIDECAR_V1_UPSTREAM"] = upstream or "https://integrate.api.nvidia.com/v1"
+
+    def to_db_dict(self) -> dict:
+        """Serialize to dict for system_config storage."""
+        result = {}
+        for key, value in asdict(self).items():
+            if isinstance(value, bool):
+                result[key] = "true" if value else "false"
+            elif isinstance(value, (int, float)):
+                result[key] = str(value)
+            else:
+                result[key] = value
+        return result
+
+    @classmethod
+    def merge_db(cls, base: "Config", db_config: dict) -> "Config":
+        """Merge DB config into base config (env vars already applied to base)."""
+        for key, value in base.__dict__.items():
+            if key in db_config and key not in os.environ:
+                # DB values only apply when no env var override
+                setattr(base, key, type(value)(db_config[key]))
+        return base
+
+
+# Singleton
+config = Config.from_env()