Gracefully handle missing pyotp so backend always starts

backend/app/services/auto_login_service.py

@@ -198,7 +198,10 @@ def _perform_zerodha_login(
     request_id = login_data["data"]["request_id"]
 
     # Step 2: TOTP — don't follow redirect automatically
-    import pyotp  # imported here so missing package doesn't crash startup
+    try:
+        import pyotp
+    except ImportError:
+        raise AutoLoginError("pyotp is not installed on the server. Run: pip install pyotp==2.9.0")
     totp_value = pyotp.TOTP(totp_secret).now()
     twofa_resp = session.post(
         KITE_TWOFA_ENDPOINT,