fix(project): stabilize python3 tests and app shutdown

Use python3/venv consistently for local test execution and
make package discovery deterministic for pytest.

Also migrate FastAPI shutdown handling to lifespan to remove
deprecation warnings while preserving cleanup behavior.

app/main.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import dataclasses
+from contextlib import asynccontextmanager
 
 from fastapi import FastAPI, HTTPException, Request
 from fastapi.responses import HTMLResponse
@@ -13,12 +14,23 @@ from app.services import PortScanner
 from app.storage import Storage
 from app.tunnel_manager import TunnelManager
 
-app = FastAPI(title="Gradio Tunnel Dashboard")
 policy = TunnelPolicy.load()
 storage = Storage.from_env()
 scanner = PortScanner(policy=policy, storage=storage)
 manager = TunnelManager(storage=storage)
 
+
+@asynccontextmanager
+async def lifespan(_: FastAPI):
+    try:
+        yield
+    finally:
+        manager.shutdown()
+        storage.close()
+
+
+app = FastAPI(title="Gradio Tunnel Dashboard", lifespan=lifespan)
+
 app.mount("/static", StaticFiles(directory="app/static"), name="static")
 templates = Jinja2Templates(directory="app/templates")
 
@@ -99,8 +111,3 @@ async def stop_tunnel(port: int) -> dict[str, bool]:
         raise HTTPException(status_code=404, detail="Tunnel not running.")
     return {"stopped": True}
 
-
-@app.on_event("shutdown")
-def shutdown_event() -> None:
-    manager.shutdown()
-    storage.close()