chore: cleanup repo and enhance validation

- Add .gitignore (.DS_Store, .vscode, __pycache__)
- Remove stale .gitkeep files (directories have content now)
- Expand schema.toml to document all 6 content types (agent, hand, integration, skill, plugin)
- Add plugin validation and contribution guide
- Add id/name vs directory name consistency checks
- Add cross-type routing alias collision detection (14 warnings found)

.gitignore

@@ -0,0 +1,5 @@
+.DS_Store
+.vscode/
+__pycache__/
+*.pyc
+.env