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/services/provider/__init__.py

@@ -0,0 +1,45 @@
+"""
+Provider 服务模块
+
+包含 Provider 管理、格式处理、传输层等功能。
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from src.services.provider.format import normalize_endpoint_signature
+    from src.services.provider.service import ProviderService
+    from src.services.provider.transport import build_provider_url
+
+__all__ = [
+    "ProviderService",
+    "normalize_endpoint_signature",
+    "build_provider_url",
+]
+
+
+def __getattr__(name: str) -> Any:
+    """Lazy attribute access to avoid import-time side effects.
+
+    Importing `src.services.provider` should not eagerly import the whole provider
+    service stack (which can create circular imports during test collection).
+    """
+
+    if name == "ProviderService":
+        from src.services.provider.service import ProviderService as _ProviderService
+
+        return _ProviderService
+    if name == "normalize_endpoint_signature":
+        from src.services.provider.format import (
+            normalize_endpoint_signature as _normalize_endpoint_signature,
+        )
+
+        return _normalize_endpoint_signature
+    if name == "build_provider_url":
+        from src.services.provider.transport import build_provider_url as _build_provider_url
+
+        return _build_provider_url
+
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")