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/models/status_snapshot.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class OAuthStatusSnapshotResponse(BaseModel):
+    code: str = Field(default="none", description="OAuth 状态代码")
+    label: str | None = Field(default=None, description="OAuth 状态标签")
+    reason: str | None = Field(default=None, description="OAuth 状态原因")
+    expires_at: int | None = Field(default=None, description="OAuth 过期时间（Unix 时间戳）")
+    invalid_at: int | None = Field(default=None, description="OAuth 失效时间（Unix 时间戳）")
+    source: str | None = Field(default=None, description="OAuth 状态来源")
+    requires_reauth: bool = Field(default=False, description="是否需要重新授权")
+    expiring_soon: bool = Field(default=False, description="是否即将过期")
+
+
+class AccountStatusSnapshotResponse(BaseModel):
+    code: str = Field(default="ok", description="账号状态代码")
+    label: str | None = Field(default=None, description="账号状态标签")
+    reason: str | None = Field(default=None, description="账号状态原因")
+    blocked: bool = Field(default=False, description="是否为账号级阻塞")
+    source: str | None = Field(default=None, description="账号状态来源")
+    recoverable: bool = Field(default=False, description="是否为可恢复状态")
+
+
+class QuotaStatusSnapshotResponse(BaseModel):
+    code: str = Field(default="unknown", description="额度状态代码")
+    label: str | None = Field(default=None, description="额度状态标签")
+    reason: str | None = Field(default=None, description="额度状态原因")
+    exhausted: bool = Field(default=False, description="额度是否耗尽")
+    usage_ratio: float | None = Field(default=None, description="额度使用比例 [0, 1]")
+    updated_at: int | None = Field(default=None, description="额度刷新时间（Unix 时间戳）")
+    reset_seconds: float | None = Field(default=None, description="距离重置剩余秒数")
+    plan_type: str | None = Field(default=None, description="额度读取到的套餐类型")
+
+
+class ProviderKeyStatusSnapshotResponse(BaseModel):
+    oauth: OAuthStatusSnapshotResponse = Field(default_factory=OAuthStatusSnapshotResponse)
+    account: AccountStatusSnapshotResponse = Field(default_factory=AccountStatusSnapshotResponse)
+    quota: QuotaStatusSnapshotResponse = Field(default_factory=QuotaStatusSnapshotResponse)