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/behavior.py

@@ -0,0 +1,60 @@
+"""Provider behavior 薄封装。
+
+对外保持既有调用接口，内部统一委托给 core.api_format.capabilities 中的 provider registry。
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from src.core.api_format.capabilities import (
+    get_provider_behavior_variants,
+    register_provider_behavior_variant,
+)
+from src.core.provider_types import normalize_provider_type
+from src.services.provider.envelope import ProviderEnvelope, get_provider_envelope
+
+
+@dataclass(frozen=True, slots=True)
+class ProviderBehavior:
+    provider_type: str
+    envelope: ProviderEnvelope | None
+    same_format_variant: str | None
+    cross_format_variant: str | None
+
+
+def register_behavior_variant(
+    provider_type: str,
+    *,
+    same_format: bool = False,
+    cross_format: bool = False,
+) -> None:
+    """兼容入口：注册 provider 的格式变体标志，真实存储位于 core registry。"""
+    register_provider_behavior_variant(
+        provider_type,
+        same_format=same_format,
+        cross_format=cross_format,
+    )
+
+
+def get_provider_behavior(
+    *,
+    provider_type: str | None,
+    endpoint_sig: str | None,
+) -> ProviderBehavior:
+    pt = normalize_provider_type(provider_type)
+    envelope = get_provider_envelope(provider_type=pt, endpoint_sig=endpoint_sig)
+    same_format_variant, cross_format_variant = get_provider_behavior_variants(
+        provider_type=pt,
+        endpoint_sig=endpoint_sig or "",
+    )
+
+    return ProviderBehavior(
+        provider_type=pt,
+        envelope=envelope,
+        same_format_variant=same_format_variant,
+        cross_format_variant=cross_format_variant,
+    )
+
+
+__all__ = ["ProviderBehavior", "get_provider_behavior", "register_behavior_variant"]