docs(plugins): fix stale sidebar example — 'workflow'/'trigger' are retired kinds

The Studio sidebar-group example listed metadata kinds retired by
ADR-0020 (workflow) and ADR-0088 (trigger); use flow + job instead.
Found via the docs-drift check on #2628.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G6pPpRszk9cD3SxcKNFMWs

Author: claude

content/docs/plugins/development.mdx

@@ -393,7 +393,7 @@ export const manifest = defineStudioPlugin({
       key: 'automation',
       label: 'Automation',
       icon: 'workflow',
-      metadataTypes: ['flow', 'trigger', 'workflow'],
+      metadataTypes: ['flow', 'job'], // ADR-0020/0088: 'workflow' and 'trigger' are retired kinds
       order: 30,
     }],