Add 5 community components to Useful Components

[costajohnt]

Adds five new community components to the Useful Components section:

• ink-timer - Timer, countdown, and stopwatch hooks and components
• ink-tree-view - Tree view with expand/collapse, keyboard navigation, and selection
• ink-combobox - Combobox input with fuzzy search and dropdown
• ink-file-picker - File picker with directory navigation and multi-select
• ink-json-viewer - Interactive, collapsible JSON tree viewer with syntax coloring

All packages are published on npm, have CI, comprehensive READMEs with demo GIFs, and TypeScript support.