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/connectors.json

@@ -31,14 +31,11 @@
       "files": [
         {
           "path": "gmail_mcp_server.py",
-          "sha256": "53e6cdbc4ff40a095d29f7538ec23ac8fc10fb83cb28496bb28a83e7c49deaae",
-          "size": 47833
+          "sha256": "e96568dda3d0198be0a34092458dac2aaafee4a7e282a3fb427923f517e536e3",
+          "size": 47789
         },
         {
-          "path": "gmail_oauth_setup.py",
-          "sha256": "e488acb289c43a3e6d541140d254451ac5688c0014e8959619375b564afe8748",
-          "size": 3627
-        },
+          "path": "icon_lg.svg",
         {
           "path": "icon_lg.svg",
           "sha256": "93c8d9c8dae96f0206e5ae3fcfe89dff3a08553ed48badf504a5abd09f5596b0",
@@ -51,8 +48,8 @@
         },
         {
           "path": "requirements.txt",
-          "sha256": "3f659cc5e5f0543f132699b06ccf9016ffe9afb40f9df4d110e0445b8d20f63e",
-          "size": 82
+          "sha256": "41a908f999095b052865efdcf793cfe7b032a3609c0cdd9f7711b2af5b3b7827",
+          "size": 54
         }
       ]
     },
@@ -85,14 +82,11 @@
       "files": [
         {
           "path": "gcal_mcp_server.py",
-          "sha256": "87b44a407feac90ed073997bd0a558c7002eec0c408d50c45da7d99011dd6107",
-          "size": 38203
+          "sha256": "c526751c8891a8d97ba37d14da282d223be7cd061eb67c76cea6a12672921db0",
+          "size": 38177
         },
         {
-          "path": "gcal_oauth_setup.py",
-          "sha256": "4abbfcf6af50cc55ca00d283353b417acc6fee7720aa10abb0fbaa0e4aa79900",
-          "size": 3430
-        },
+          "path": "verify.py",
         {
           "path": "verify.py",
           "sha256": "d994ae435d8a5a3d9cdc85c8f73805a877c1a8818637b2912f6c31c693fdded4",
@@ -110,8 +104,8 @@
         },
         {
           "path": "requirements.txt",
-          "sha256": "3f659cc5e5f0543f132699b06ccf9016ffe9afb40f9df4d110e0445b8d20f63e",
-          "size": 82
+          "sha256": "41a908f999095b052865efdcf793cfe7b032a3609c0cdd9f7711b2af5b3b7827",
+          "size": 54
         }
       ]
     },