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/provider_context.py

@@ -0,0 +1,116 @@
+"""Helpers for resolving provider metadata without touching detached ORM relations."""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+
+def _safe_getattr(obj: Any, attr: str) -> Any:
+    if obj is None:
+        return None
+    try:
+        return getattr(obj, attr)
+    except Exception:
+        # Intentionally broad: ORM objects may raise DetachedInstanceError,
+        # MissingGreenlet, or other SQLAlchemy errors when accessing
+        # lazy-loaded attributes on expired/detached objects.
+        return None
+
+
+def _normalize_text(value: Any) -> str:
+    return str(value or "").strip()
+
+
+def _extract_provider_id(*, endpoint: Any | None = None, key: Any | None = None) -> str | None:
+    for source in (key, endpoint):
+        provider_id = _normalize_text(_safe_getattr(source, "provider_id"))
+        if provider_id:
+            return provider_id
+
+    for provider_obj in (_safe_getattr(endpoint, "provider"), _safe_getattr(key, "provider")):
+        provider_id = _normalize_text(_safe_getattr(provider_obj, "id"))
+        if provider_id:
+            return provider_id
+
+    return None
+
+
+_SNAPSHOT_CACHE: dict[str, tuple[float, dict[str, Any]]] = {}
+_SNAPSHOT_TTL: float = 30.0  # seconds
+
+
+def _load_provider_snapshot(provider_id: str | None) -> dict[str, Any] | None:
+    normalized_id = _normalize_text(provider_id)
+    if not normalized_id:
+        return None
+
+    now = time.monotonic()
+    cached = _SNAPSHOT_CACHE.get(normalized_id)
+    if cached is not None and (now - cached[0]) < _SNAPSHOT_TTL:
+        return cached[1]
+
+    from src.database import create_session
+    from src.models.database import Provider
+
+    with create_session() as db:
+        row = db.query(Provider).filter(Provider.id == normalized_id).first()
+        if row is None:
+            return None
+        snapshot = {
+            "provider_type": _safe_getattr(row, "provider_type"),
+            "proxy": _safe_getattr(row, "proxy"),
+        }
+        _SNAPSHOT_CACHE[normalized_id] = (now, snapshot)
+        return snapshot
+
+
+def resolve_provider_type(
+    *,
+    endpoint: Any | None = None,
+    key: Any | None = None,
+    explicit_provider_type: str | None = None,
+    decrypted_auth_config: dict[str, Any] | None = None,
+) -> str | None:
+    provider_type = _normalize_text(explicit_provider_type).lower()
+    if provider_type:
+        return provider_type
+
+    for source in (endpoint, key):
+        provider_type = _normalize_text(_safe_getattr(source, "provider_type")).lower()
+        if provider_type:
+            return provider_type
+
+    for provider_obj in (_safe_getattr(endpoint, "provider"), _safe_getattr(key, "provider")):
+        provider_type = _normalize_text(_safe_getattr(provider_obj, "provider_type")).lower()
+        if provider_type:
+            return provider_type
+
+    if isinstance(decrypted_auth_config, dict):
+        provider_type = _normalize_text(decrypted_auth_config.get("provider_type")).lower()
+        if provider_type:
+            return provider_type
+
+    snapshot = _load_provider_snapshot(_extract_provider_id(endpoint=endpoint, key=key))
+    provider_type = _normalize_text((snapshot or {}).get("provider_type")).lower()
+    return provider_type or None
+
+
+def resolve_provider_proxy(
+    *,
+    endpoint: Any | None = None,
+    key: Any | None = None,
+) -> dict[str, Any] | None:
+    for source in (endpoint, key):
+        provider_proxy = _safe_getattr(source, "provider_proxy")
+        if isinstance(provider_proxy, dict):
+            return provider_proxy
+
+    for provider_obj in (_safe_getattr(endpoint, "provider"), _safe_getattr(key, "provider")):
+        provider_proxy = _safe_getattr(provider_obj, "proxy")
+        if isinstance(provider_proxy, dict):
+            return provider_proxy
+
+    snapshot = _load_provider_snapshot(_extract_provider_id(endpoint=endpoint, key=key))
+    provider_proxy = (snapshot or {}).get("proxy")
+    return provider_proxy if isinstance(provider_proxy, dict) else None