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/scheduling/__init__.py

@@ -0,0 +1,30 @@
+"""调度系统（候选/排序/亲和性/并发检查）。
+
+原 `src.services.cache` 中与调度相关的代码已迁移到此包；
+`src.services.cache` 现在只保留通用缓存 backend/sync/*_cache。
+"""
+
+from src.services.scheduling.affinity_manager import CacheAffinityManager, get_affinity_manager
+from src.services.scheduling.aware_scheduler import (
+    CacheAwareScheduler,
+    ConcurrencySnapshot,
+    ProviderCandidate,
+    get_cache_aware_scheduler,
+)
+from src.services.scheduling.candidate_builder import CandidateBuilder
+from src.services.scheduling.candidate_sorter import CandidateSorter
+from src.services.scheduling.concurrency_checker import ConcurrencyChecker
+from src.services.scheduling.scheduling_config import SchedulingConfig
+
+__all__ = [
+    "CacheAffinityManager",
+    "CandidateBuilder",
+    "CandidateSorter",
+    "CacheAwareScheduler",
+    "ConcurrencyChecker",
+    "ConcurrencySnapshot",
+    "ProviderCandidate",
+    "SchedulingConfig",
+    "get_affinity_manager",
+    "get_cache_aware_scheduler",
+]