refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

_deprecated_py_src/api/admin/stats/quota.py

@@ -0,0 +1,90 @@
+"""Admin quota usage stats routes."""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+from typing import Any
+
+from fastapi import APIRouter, Depends, Request
+from sqlalchemy.orm import Session
+
+from src.api.base.admin_adapter import AdminApiAdapter
+from src.api.base.context import ApiRequestContext
+from src.config.constants import CacheTTL
+from src.core.enums import ProviderBillingType
+from src.database import get_db
+from src.models.database import Provider
+from src.utils.cache_decorator import cache_result
+
+from .common import pipeline
+
+router = APIRouter()
+
+
+class AdminQuotaUsageAdapter(AdminApiAdapter):
+    @cache_result(
+        key_prefix="admin:stats:providers:quota_usage",
+        ttl=CacheTTL.ADMIN_USAGE_AGGREGATION,
+        user_specific=False,
+    )
+    async def handle(self, context: ApiRequestContext) -> Any:  # type: ignore[override]
+        db = context.db
+        providers = (
+            db.query(Provider)
+            .filter(
+                (Provider.billing_type == ProviderBillingType.MONTHLY_QUOTA)
+                | (Provider.monthly_quota_usd.isnot(None))
+            )
+            .all()
+        )
+        now = datetime.now(timezone.utc)
+
+        result = []
+        for provider in providers:
+            quota = float(provider.monthly_quota_usd or 0)
+            used = float(provider.monthly_used_usd or 0)
+            remaining = max(quota - used, 0.0)
+            usage_percent = round((used / quota) * 100, 2) if quota > 0 else 0.0
+
+            reset_at = provider.quota_last_reset_at
+            if reset_at:
+                days_elapsed = max(1, (now - reset_at).days)
+            else:
+                days_elapsed = max(1, now.day - 1)
+
+            daily_rate = used / days_elapsed if used > 0 else 0.0
+            estimated_exhaust_at = None
+            if daily_rate > 0 and remaining > 0:
+                estimated_exhaust_at = now + timedelta(days=remaining / daily_rate)
+            if provider.quota_expires_at:
+                if not estimated_exhaust_at or provider.quota_expires_at < estimated_exhaust_at:
+                    estimated_exhaust_at = provider.quota_expires_at
+
+            result.append(
+                {
+                    "id": provider.id,
+                    "name": provider.name,
+                    "quota_usd": float(quota),
+                    "used_usd": float(used),
+                    "remaining_usd": float(remaining),
+                    "usage_percent": usage_percent,
+                    "quota_expires_at": (
+                        provider.quota_expires_at.isoformat() if provider.quota_expires_at else None
+                    ),
+                    "estimated_exhaust_at": (
+                        estimated_exhaust_at.isoformat() if estimated_exhaust_at else None
+                    ),
+                }
+            )
+
+        result.sort(key=lambda x: x["usage_percent"], reverse=True)
+        return {"providers": result}
+
+
+@router.get("/providers/quota-usage")
+async def get_quota_usage(
+    request: Request,
+    db: Session = Depends(get_db),
+) -> Any:
+    adapter = AdminQuotaUsageAdapter()
+    return await pipeline.run(adapter=adapter, http_request=request, db=db, mode=adapter.mode)