chore: Add .npmignore to exclude models from npm package

- npm package will be ~5.5MB instead of 200MB+
- Models download automatically on first use
- Added models-cache/ to .gitignore

.gitignore

@@ -58,6 +58,7 @@ TODO_PRIVATE.md
 
 # Models (downloaded at runtime)
 models/
+models-cache/
 
 # Development planning files (not for commit)
 PLAN.md