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/utils.py

@@ -0,0 +1,53 @@
+"""
+调度器工具函数
+
+从 CacheAwareScheduler 提取的静态工具方法。
+"""
+
+from __future__ import annotations
+
+import hashlib
+
+from sqlalchemy.orm import Session
+
+
+def affinity_hash(affinity_key: str, identifier: str) -> int:
+    """基于 affinity_key 和标识符的确定性哈希（用于同优先级内分散负载均衡）"""
+    return int(hashlib.sha256(f"{affinity_key}:{identifier}".encode()).hexdigest()[:16], 16)
+
+
+def release_db_connection_before_await(db: Session) -> None:
+    """
+    Best-effort: end a read-only transaction before awaiting async I/O.
+
+    This scheduler does a lot of async work (cache/Redis) mixed with sync SQLAlchemy reads.
+    If a SELECT has already started a transaction, the pooled connection can remain checked
+    out while we await, causing pool pressure under concurrency.
+
+    Safety:
+    - Only commits when the Session has no ORM pending changes.
+    - Temporarily disables expire_on_commit to keep already-loaded ORM objects usable.
+    """
+    try:
+        if db is None:
+            return
+        has_pending_changes = bool(db.new) or bool(db.dirty) or bool(db.deleted)
+        if has_pending_changes:
+            return
+        if not db.in_transaction():
+            return
+
+        original_expire_on_commit = getattr(db, "expire_on_commit", True)
+        db.expire_on_commit = False
+        try:
+            db.commit()
+        except Exception:
+            try:
+                db.rollback()
+            except Exception:
+                pass
+        finally:
+            db.expire_on_commit = original_expire_on_commit
+    except Exception:
+        # Never let this optimization break scheduling
+        return