pi-linkup v0.8.0

a4905b5: Expose Linkup tools as separate Pi extensions so pi config can enable or disable them individually.
7334153: Redesign all tool UIs to use structured rendering components
- web-search: ToolCallHeader, Container/Markdown/ToolFooter, collapsed/expanded states with blockquote snippets
- web-answer: ToolCallHeader, answer preview collapsed, full Markdown answer expanded with sources list
- web-fetch: ToolCallHeader, Markdown content preview matching read_url pattern (8 lines collapsed, full expanded)
- All tools: throw errors instead of returning error details, proper error display via content extraction
- All tools: use keyHint for expand hints, ToolFooter for metadata
cb71445: Redesign web search tool UI to match pi-synthetic pattern
- Use ToolCallHeader and ToolFooter from @aliou/pi-utils-ui for consistent styling
- Collapsed view shows result count with first result name and expand hint
- Expanded view shows each result with name, URL, and a 5-line blockquote snippet rendered as Markdown
- Error handling uses throw instead of returning error details, matching the pi framework convention
- Errors now display the actual error message instead of misleading “no results”
- Footer shows result count only
- Show search depth as option arg in header when non-standard

290df71: Add a Vitest-based Pi runtime harness to verify per-tool pi config loading, shared command registration, and dynamic Linkup system prompt guidance. Closes #17.