[cookbook image-captioning] Add caption streaming and perf metrics

[williamw]

Enhances the image captioning recipe with progressive NDJSON streaming, parallel processing, and performance tracking.

Key Changes

Image Captioning Recipe

• NDJSON streaming: Custom useNDJSON hook for progressive caption results without external dependencies
• Parallel processing: Multiple images processed simultaneously with individual progress tracking
• Performance metrics: TTFT (time to first token) and generation duration tracking
• Time formatting: pretty-ms library for human-readable time display (e.g., "2m 5s", "245ms")
• API improvements: Uses streamText to capture timing, streams results as newline-delimited JSON

Multi-turn Chat Recipe

• Updated documentation to highlight Streamdown for markdown/syntax highlighting
• Polished inline comments for clarity

Infrastructure

• Added workspace-level dependency catalog (pnpm-workspace.yaml)
• Added pretty-ms for time formatting
• Updated package.json files across workspace

Documentation

• Enhanced README with feature descriptions for both recipes
• Updated recipe metadata descriptions to be more concise
• Improved inline code comments throughout

Other Improvements

• Fixed theme toggle hydration warning
• Updated button styles for consistency