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/core/enums.py

@@ -0,0 +1,47 @@
+"""
+统一的枚举定义
+避免重复定义造成的不一致
+
+注意：APIFormat 架构已移除，统一使用 endpoint signature（family:kind）。
+"""
+
+from enum import Enum
+
+
+class UserRole(Enum):
+    """用户角色枚举"""
+
+    ADMIN = "admin"
+    USER = "user"
+
+
+class ProviderBillingType(Enum):
+    """提供商计费类型"""
+
+    MONTHLY_QUOTA = "monthly_quota"  # 月卡额度
+    PAY_AS_YOU_GO = "pay_as_you_go"  # 按量付费
+    FREE_TIER = "free_tier"  # 免费额度
+
+
+class AuthSource(str, Enum):
+    """认证来源枚举"""
+
+    LOCAL = "local"  # 本地认证
+    LDAP = "ldap"  # LDAP 认证
+    OAUTH = "oauth"  # OAuth 认证（账号首创来源）
+
+
+class ErrorCategory(str, Enum):
+    """错误分类枚举"""
+
+    RATE_LIMIT = "rate_limit"
+    AUTH = "auth"
+    INVALID_REQUEST = "invalid_request"
+    NOT_FOUND = "not_found"
+    CONTENT_FILTER = "content_filter"
+    CONTEXT_LENGTH = "context_length"
+    SERVER_ERROR = "server_error"
+    TIMEOUT = "timeout"
+    NETWORK = "network"
+    CANCELLED = "cancelled"
+    UNKNOWN = "unknown"