fix(starlark): code review fixes - security, robustness, and schema parsing

## Security Fixes
- manager.py: Check _update_manifest_safe return values to prevent silent failures
- manager.py: Improve temp file cleanup in _save_manifest to prevent leaks
- manager.py: Fix uninstall order (manifest → memory → disk) for consistency
- api_v3.py: Add path traversal validation in uninstall endpoint
- api_v3.py: Implement atomic writes for manifest files with temp + rename
- pixlet_renderer.py: Relax config validation to only block dangerous shell metacharacters

## Frontend Robustness
- plugins_manager.js: Add safeLocalStorage wrapper for restricted contexts (private browsing)
- starlark_config.html: Scope querySelector to container to prevent modal conflicts

## Schema Parsing Improvements
- pixlet_renderer.py: Indentation-aware get_schema() extraction (handles nested functions)
- pixlet_renderer.py: Handle quoted defaults with commas (e.g., "New York, NY")
- tronbyte_repository.py: Validate file_name is string before path traversal checks

## Dependencies
- requirements.txt: Update Pillow (10.4.0), PyYAML (6.0.2), requests (2.32.0)

## Documentation
- docs/STARLARK_APPS_GUIDE.md: Comprehensive guide explaining:
  - How Starlark apps work
  - That apps come from Tronbyte (not LEDMatrix)
  - Installation, configuration, troubleshooting
  - Links to upstream projects

All changes improve security, reliability, and user experience.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

plugin-repos/starlark-apps/tronbyte_repository.py

@@ -462,6 +462,12 @@ class TronbyteRepository:
                 for file_item in dir_data:
                     if file_item.get('type') == 'file':
                         file_name = file_item.get('name')
+
+                        # Ensure file_name is a non-empty string before validation
+                        if not file_name or not isinstance(file_name, str):
+                            logger.warning(f"Skipping file with invalid name in {dir_name}: {file_item}")
+                            continue
+
                         # Validate filename for path traversal
                         if '..' in file_name or '/' in file_name or '\\' in file_name:
                             logger.warning(f"Skipping potentially unsafe file: {file_name}")