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/api/handlers/__init__.py

@@ -0,0 +1,99 @@
+"""
+API Handlers - 请求处理器
+
+按 API 格式组织的 Adapter 和 Handler：
+- Adapter: 请求验证、格式转换、错误处理
+- Handler: 业务逻辑、调用 Provider、记录用量
+
+支持的格式：
+- claude: Claude Chat API (/v1/messages)
+- claude_cli: Claude CLI 透传模式
+- openai: OpenAI Chat API (/v1/chat/completions)
+- openai_cli: OpenAI CLI 透传模式
+
+注意：Handler 基类和具体 Handler 使用延迟导入以避免循环依赖。
+"""
+
+# Adapter 基类（不会引起循环导入，可以直接导入）
+from src.api.handlers.base import (
+    ChatAdapterBase,
+    CliAdapterBase,
+)
+
+__all__ = [
+    # Adapter 基类
+    "ChatAdapterBase",
+    "CliAdapterBase",
+    # Handler 基类（延迟导入）
+    "ChatHandlerBase",
+    "CliMessageHandlerBase",
+    "BaseMessageHandler",
+    "MessageHandlerProtocol",
+    "MessageTelemetry",
+    "StreamContext",
+    # Claude
+    "ClaudeChatAdapter",
+    "ClaudeTokenCountAdapter",
+    "build_claude_adapter",
+    "ClaudeChatHandler",
+    # Claude CLI
+    "ClaudeCliAdapter",
+    "ClaudeCliMessageHandler",
+    # OpenAI
+    "OpenAIChatAdapter",
+    "OpenAIChatHandler",
+    # OpenAI CLI
+    "OpenAICliAdapter",
+    "OpenAICliMessageHandler",
+]
+
+# 延迟导入映射表
+_LAZY_IMPORTS = {
+    # Handler 基类
+    "ChatHandlerBase": ("src.api.handlers.base.chat_handler_base", "ChatHandlerBase"),
+    "CliMessageHandlerBase": (
+        "src.api.handlers.base.cli_handler_base",
+        "CliMessageHandlerBase",
+    ),
+    "StreamContext": ("src.api.handlers.base.cli_handler_base", "StreamContext"),
+    "BaseMessageHandler": ("src.api.handlers.base.base_handler", "BaseMessageHandler"),
+    "MessageHandlerProtocol": (
+        "src.api.handlers.base.base_handler",
+        "MessageHandlerProtocol",
+    ),
+    "MessageTelemetry": ("src.api.handlers.base.base_handler", "MessageTelemetry"),
+    # Claude
+    "ClaudeChatAdapter": ("src.api.handlers.claude.adapter", "ClaudeChatAdapter"),
+    "ClaudeTokenCountAdapter": (
+        "src.api.handlers.claude.adapter",
+        "ClaudeTokenCountAdapter",
+    ),
+    "build_claude_adapter": ("src.api.handlers.claude.adapter", "build_claude_adapter"),
+    "ClaudeChatHandler": ("src.api.handlers.claude.handler", "ClaudeChatHandler"),
+    # Claude CLI
+    "ClaudeCliAdapter": ("src.api.handlers.claude_cli.adapter", "ClaudeCliAdapter"),
+    "ClaudeCliMessageHandler": (
+        "src.api.handlers.claude_cli.handler",
+        "ClaudeCliMessageHandler",
+    ),
+    # OpenAI
+    "OpenAIChatAdapter": ("src.api.handlers.openai.adapter", "OpenAIChatAdapter"),
+    "OpenAIChatHandler": ("src.api.handlers.openai.handler", "OpenAIChatHandler"),
+    # OpenAI CLI
+    "OpenAICliAdapter": ("src.api.handlers.openai_cli.adapter", "OpenAICliAdapter"),
+    "OpenAICliMessageHandler": (
+        "src.api.handlers.openai_cli.handler",
+        "OpenAICliMessageHandler",
+    ),
+}
+
+
+def __getattr__(name: str) -> None:
+    """延迟导入以避免循环依赖"""
+    if name in _LAZY_IMPORTS:
+        module_path, attr_name = _LAZY_IMPORTS[name]
+        import importlib
+
+        module = importlib.import_module(module_path)
+        return getattr(module, attr_name)
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")