feat: expire offline work with sessions (#399)

src/main.py

@@ -875,10 +875,13 @@ async def fresh_authorization(payload: FreshAuthorization, request: Request):
 @app.get("/api/v1/session")
 async def session_status(request: Request):
     session = request.state.dashboard_session
-    return {
+    payload = {
         "authenticated": session is not None,
         "csrf_token": session.csrf if session is not None else "",
     }
+    if session is not None:
+        payload["expires_at"] = session.expires_at
+    return payload
 
 
 def _today_store() -> TodayStore: