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/model/__init__.py

@@ -0,0 +1,68 @@
+"""
+模型服务模块
+
+包含模型管理、成本计算等功能。
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from src.services.model.availability import ModelAvailabilityQuery
+    from src.services.model.cost import ModelCostService
+    from src.services.model.fetch_scheduler import ModelFetchScheduler, get_model_fetch_scheduler
+    from src.services.model.global_model import GlobalModelService
+    from src.services.model.service import ModelService
+
+__all__ = [
+    "ModelService",
+    "GlobalModelService",
+    "ModelCostService",
+    "ModelAvailabilityQuery",
+    "ModelFetchScheduler",
+    "get_model_fetch_scheduler",
+]
+
+
+def __getattr__(name: str) -> Any:
+    """Lazy attribute access to avoid import-time side effects.
+
+    Importing `src.services.model` should not eagerly import the whole model
+    service stack (scheduler/services), which can create circular imports during
+    test collection.
+    """
+
+    if name == "ModelAvailabilityQuery":
+        from src.services.model.availability import ModelAvailabilityQuery as _ModelAvailabilityQuery
+
+        return _ModelAvailabilityQuery
+
+    if name == "ModelCostService":
+        from src.services.model.cost import ModelCostService as _ModelCostService
+
+        return _ModelCostService
+
+    if name == "ModelFetchScheduler":
+        from src.services.model.fetch_scheduler import ModelFetchScheduler as _ModelFetchScheduler
+
+        return _ModelFetchScheduler
+
+    if name == "get_model_fetch_scheduler":
+        from src.services.model.fetch_scheduler import (
+            get_model_fetch_scheduler as _get_model_fetch_scheduler,
+        )
+
+        return _get_model_fetch_scheduler
+
+    if name == "GlobalModelService":
+        from src.services.model.global_model import GlobalModelService as _GlobalModelService
+
+        return _GlobalModelService
+
+    if name == "ModelService":
+        from src.services.model.service import ModelService as _ModelService
+
+        return _ModelService
+
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")