chore: sync generated files and fix agentmail metadata

- Fixed agentmail/SKILL.md description (was 305 chars, now concise)
- Added risk: safe and source: community labels
- Regenerated skills_index.json (970 skills)
- Updated README.md with latest skill count
- Regenerated CATALOG.md, data/catalog.json, data/bundles.json

Post-merge fixes for PR #183 following MAINTENANCE.md procedures.

data/bundles.json

@@ -6,6 +6,7 @@
       "skills": [
         "3d-web-experience",
         "agent-framework-azure-ai-py",
+        "agentmail",
         "algolia-search",
         "android-jetpack-compose-expert",
         "android_ui_verification",