feat: Advanced settings - custom uvx path, server source override, health check

- Add UvxPath, ServerSourceOverride, DevModeForceRefresh to McpSettings
- Rebuild McpAdvancedSection with Server Configuration, Health Check, Settings, Diagnostics sections
- Extract ServerEntryBuilder to share config generation logic between JsonFileConfigWriter and ClaudeCliConfigWriter
- Support custom uvx path and --from for local server development
- Add --no-cache --refresh dev mode for avoiding stale uvx cache
- Add TCP health check button with visual status indicator
- Include server config info in Copy Diagnostics output
- Add __pycache__/ and *.pyc to .gitignore, remove tracked __pycache__ files

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>