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/internal/tunnel.py

@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+import asyncio
+from typing import Any
+
+from fastapi import APIRouter, HTTPException, Request
+from pydantic import BaseModel, Field
+
+from src.services.proxy_node.service import ProxyNodeService, build_heartbeat_ack
+
+from .common import ensure_loopback
+
+router = APIRouter(
+    prefix="/api/internal/tunnel",
+    tags=["Internal - Tunnel"],
+    include_in_schema=False,
+)
+
+
+class TunnelHeartbeatRequest(BaseModel):
+    node_id: str = Field(..., min_length=1, max_length=36)
+    heartbeat_interval: int | None = Field(None, ge=5, le=600)
+    active_connections: int | None = Field(None, ge=0)
+    total_requests: int | None = Field(None, ge=0)
+    avg_latency_ms: float | None = Field(None, ge=0)
+    failed_requests: int | None = Field(None, ge=0)
+    dns_failures: int | None = Field(None, ge=0)
+    stream_errors: int | None = Field(None, ge=0)
+    proxy_metadata: dict[str, Any] | None = None
+    proxy_version: str | None = Field(None, max_length=20)
+
+
+class TunnelNodeStatusRequest(BaseModel):
+    node_id: str = Field(..., min_length=1, max_length=36)
+    connected: bool
+    conn_count: int = Field(0, ge=0)
+
+
+@router.post("/heartbeat")
+async def tunnel_heartbeat(
+    request: Request, payload: TunnelHeartbeatRequest
+) -> dict[str, Any]:
+    ensure_loopback(request)
+
+    def _sync_apply() -> dict[str, Any]:
+        from src.database import create_session
+
+        db = create_session()
+        try:
+            node = ProxyNodeService.heartbeat(
+                db,
+                node_id=payload.node_id,
+                heartbeat_interval=payload.heartbeat_interval,
+                active_connections=payload.active_connections,
+                total_requests=payload.total_requests,
+                avg_latency_ms=payload.avg_latency_ms,
+                failed_requests=payload.failed_requests,
+                dns_failures=payload.dns_failures,
+                stream_errors=payload.stream_errors,
+                proxy_metadata=payload.proxy_metadata,
+                proxy_version=payload.proxy_version,
+            )
+            return build_heartbeat_ack(node)
+        finally:
+            db.close()
+
+    try:
+        return await asyncio.to_thread(_sync_apply)
+    except Exception as exc:
+        raise HTTPException(status_code=500, detail=f"heartbeat sync failed: {exc}") from exc
+
+
+@router.post("/node-status")
+async def tunnel_node_status(
+    request: Request, payload: TunnelNodeStatusRequest
+) -> dict[str, Any]:
+    ensure_loopback(request)
+
+    def _sync_apply() -> dict[str, Any]:
+        from src.database import create_session
+
+        db = create_session()
+        try:
+            node = ProxyNodeService.update_tunnel_status(
+                db,
+                node_id=payload.node_id,
+                connected=payload.connected,
+                conn_count=payload.conn_count,
+            )
+            return {"updated": node is not None}
+        finally:
+            db.close()
+
+    try:
+        return await asyncio.to_thread(_sync_apply)
+    except Exception as exc:
+        raise HTTPException(status_code=500, detail=f"node status sync failed: {exc}") from exc