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/billing/cache.py

@@ -0,0 +1,130 @@
+"""
+Billing in-process cache.
+
+This module provides a small TTL cache for billing rule lookups and other
+high-read, low-churn billing configuration objects.
+
+Important:
+- Keep cached values *session-agnostic*. Avoid caching SQLAlchemy ORM objects
+  bound to a specific Session; prefer plain dataclasses / dicts.
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+
+class BillingCache:
+    """
+    Simple TTL + LRU cache.
+
+    - TTL: 300s (5 minutes)
+    - Max entries per cache: 2048 (evict oldest on overflow)
+    """
+
+    TTL_SECONDS = 300
+    MAX_ENTRIES = 2048
+
+    _rule_cache: dict[str, tuple[Any, float]] = {}
+    _collector_cache: dict[str, tuple[Any, float]] = {}
+    _default_rule_cache: dict[str, tuple[Any, float]] = {}
+
+    # ----------------------------
+    # Rule cache
+    # ----------------------------
+    @classmethod
+    def get_rule(cls, cache_key: str) -> Any | None:
+        return cls._get(cls._rule_cache, cache_key)
+
+    @classmethod
+    def set_rule(cls, cache_key: str, value: Any) -> None:
+        cls._set(cls._rule_cache, cache_key, value)
+
+    # ----------------------------
+    # Default-rule cache
+    # ----------------------------
+    @classmethod
+    def get_default_rule(cls, cache_key: str) -> Any | None:
+        return cls._get(cls._default_rule_cache, cache_key)
+
+    @classmethod
+    def set_default_rule(cls, cache_key: str, value: Any) -> None:
+        cls._set(cls._default_rule_cache, cache_key, value)
+
+    # ----------------------------
+    # Collector cache (reserved)
+    # ----------------------------
+    @classmethod
+    def get_collectors(cls, cache_key: str) -> Any | None:
+        return cls._get(cls._collector_cache, cache_key)
+
+    @classmethod
+    def set_collectors(cls, cache_key: str, value: Any) -> None:
+        cls._set(cls._collector_cache, cache_key, value)
+
+    # ----------------------------
+    # Invalidation
+    # ----------------------------
+    @classmethod
+    def invalidate_all(cls) -> None:
+        cls._rule_cache.clear()
+        cls._collector_cache.clear()
+        cls._default_rule_cache.clear()
+
+    @classmethod
+    def invalidate_model(cls, model_name: str) -> None:
+        """
+        Invalidate cache entries referencing a model name.
+
+        Note:
+        - This is best-effort string matching (cache key format must include model_name).
+        """
+        cls._invalidate_by_substring(cls._rule_cache, model_name)
+        cls._invalidate_by_substring(cls._default_rule_cache, model_name)
+
+    # ----------------------------
+    # Internal helpers
+    # ----------------------------
+    @classmethod
+    def _get(cls, cache: dict[str, tuple[Any, float]], key: str) -> Any | None:
+        item = cache.get(key)
+        if item is None:
+            return None
+        value, ts = item
+        if time.time() - ts < cls.TTL_SECONDS:
+            return value
+        # expired
+        try:
+            del cache[key]
+        except KeyError:
+            pass
+        return None
+
+    @classmethod
+    def _set(cls, cache: dict[str, tuple[Any, float]], key: str, value: Any) -> None:
+        """Set with LRU eviction when cache exceeds MAX_ENTRIES."""
+        now = time.time()
+        cache[key] = (value, now)
+
+        # Evict oldest entries if over limit
+        if len(cache) > cls.MAX_ENTRIES:
+            cls._evict_oldest(cache, cls.MAX_ENTRIES // 4)
+
+    @classmethod
+    def _evict_oldest(cls, cache: dict[str, tuple[Any, float]], count: int) -> None:
+        """Evict the oldest `count` entries from cache."""
+        if not cache or count <= 0:
+            return
+        # Sort by timestamp (oldest first) and remove
+        sorted_keys = sorted(cache.keys(), key=lambda k: cache[k][1])
+        for k in sorted_keys[:count]:
+            cache.pop(k, None)
+
+    @staticmethod
+    def _invalidate_by_substring(cache: dict[str, tuple[Any, float]], needle: str) -> None:
+        if not needle:
+            return
+        keys = [k for k in cache.keys() if needle in k]
+        for k in keys:
+            cache.pop(k, None)