gmail: add OAuth deliver block to manifest + index

connector.json: auth.deliver declares {as, format, path} so Skald
can write the Google authorized_user JSON without hardcoding paths.

connectors.json: gmail entry gains auth {type, provider, scopes}
for UI badge rendering without downloading the full manifest.

No changes to email, ssh, or tavily connectors.

connectors/gmail/connector.json

@@ -52,6 +52,11 @@
     "scopes": [
       "https://www.googleapis.com/auth/gmail.modify",
       "https://www.googleapis.com/auth/gmail.labels"
-    ]
+    ],
+    "deliver": {
+      "as": "file",
+      "format": "google_authorized_user",
+      "path": "{secrets}/gmail_creds.json"
+    }
   }
 }