Purge standalone OAuth setup for Gmail and Gcal

- Deleted gmail_oauth_setup.py and gcal_oauth_setup.py (Skald handles OAuth)
- Removed google-auth-oauthlib dependency from requirements.txt and connector.json
- Simplified setup_instructions to point to Skald's OAuth flow
- Updated docstrings and error messages in *_mcp_server.py (no more refs to
  *_oauth_setup.py, point to Skald OAuth / env-var instead)
- connectors.json: removed oauth_setup.py from files[], updated sha256 hashes

connectors/gcal/gcal_mcp_server.py

@@ -13,7 +13,6 @@ Capabilities (callable as `mcp__gcal__<tool>`):
 
 Skald mode: Skald injects credentials via GCAL_CREDS_JSON env var (authorized_user JSON).
 Standalone mode: reads from GOOGLE_CREDS_PATH or ./secrets/google_creds.json.
-Run scripts/gcal_oauth_setup.py to (re-)authenticate (standalone).
 
 Required OAuth scopes:
   https://www.googleapis.com/auth/calendar
@@ -282,21 +281,20 @@ def _format_google_error(e: Exception, api_label: str) -> str:
     if RefreshError is not None and isinstance(e, RefreshError):
         return (
             f"Error: {api_label} API token refresh failed (the refresh token may have been revoked "
-            "or expired). Re-run scripts/gcal_oauth_setup.py to re-authenticate."
+            "or expired). Re-authenticate via Skald's OAuth flow (Sign in from the connector page)."
         )
 
     if HttpError is not None and isinstance(e, HttpError):
         status = getattr(e, "status_code", None)
         if status == 401:
             return (
-                f"Error: {api_label} API rejected the access token (401). The OAuth token is invalid "
-                "or revoked. Re-run scripts/gcal_oauth_setup.py to re-authenticate."
-            )
+            f"Error: {api_label} API rejected the access token (401). The OAuth token is invalid "
+            "or revoked. Re-authenticate via Skald's OAuth flow (Sign in from the connector page)."            )
         if status == 403:
             return (
                 f"Error: {api_label} API returned 403 Forbidden. The OAuth scopes granted are "
                 "insufficient for this operation, or the Calendar API is disabled in the Google Cloud "
-                "Console. Verify the scopes in scripts/gcal_oauth_setup.py and the API enablement."
+                "Console. Verify the scopes in the Google OAuth provider config and the API enablement."
             )
         if status == 404:
             return (
@@ -350,9 +348,8 @@ def _gcal_status(args: dict | None = None) -> str:
     except Exception as e:
         return _status_report("❌", "AUTH_OR_API_ERROR", "action needed",
             f"The Calendar API did not respond to the probe call: {_format_google_error(e, 'Calendar')}",
-            ["Run scripts/gcal_oauth_setup.py to refresh / re-issue credentials.",
+             ["Re-authenticate via Skald's OAuth flow (Sign in from the connector page).",
              "If credentials are valid, verify the Google Calendar API is enabled in the Google Cloud Console."])
-
     items = result.get("items", []) if isinstance(result, dict) else []
     primary = next((c for c in items if c.get("primary")), None)
     suffix = f"\nAccount: {primary.get('id')}" if primary else ""