Switch Gmail and Gcal to env-var OAuth delivery pattern

auth.deliver changes from as:file to as:env:
- Gmail: GMAIL_CREDS_JSON env var (Google authorized_user JSON)
- Gcal: GCAL_CREDS_JSON env var

mcp_config.env removed entirely — Skald injects the env var at runtime,
no path on disk needed.

Server scripts updated:
- Check GMAIL_CREDS_JSON / GCAL_CREDS_JSON env var first
- Use Credentials.from_authorized_user_info() instead of
  from_authorized_user_file()
- Fall back to file-based loading for standalone/legacy use
- _persist_creds only writes to disk when _creds_path is set

gcal/verify.py: support GCAL_CREDS_JSON env var with shared _check_api()

Docs (SKALD.md): updated examples, field table, connector table.

connectors/connectors.json

@@ -31,8 +31,8 @@
       "files": [
         {
           "path": "gmail_mcp_server.py",
-          "sha256": "a50d4da9621f7a4b092f4e3c5ae85dec5f466783372f78ca7e792046dc01c673",
-          "size": 46772
+          "sha256": "53e6cdbc4ff40a095d29f7538ec23ac8fc10fb83cb28496bb28a83e7c49deaae",
+          "size": 47833
         },
         {
           "path": "gmail_oauth_setup.py",
@@ -85,8 +85,8 @@
       "files": [
         {
           "path": "gcal_mcp_server.py",
-          "sha256": "0d1450ae552aba8035e608fa7785487459b9ecf0b05064c15fb5511d93ac92c1",
-          "size": 37210
+          "sha256": "87b44a407feac90ed073997bd0a558c7002eec0c408d50c45da7d99011dd6107",
+          "size": 38203
         },
         {
           "path": "gcal_oauth_setup.py",
@@ -95,8 +95,8 @@
         },
         {
           "path": "verify.py",
-          "sha256": "3bbc8c32bd320ed772972798371a39b03c3e52ce1dfd66a1493cda9e78e428e5",
-          "size": 2328
+          "sha256": "d994ae435d8a5a3d9cdc85c8f73805a877c1a8818637b2912f6c31c693fdded4",
+          "size": 3429
         },
         {
           "path": "icon_sm.svg",