Add arXiv (search, paper) and Wikipedia (search, summary) public API adapters.
- arxiv/search: search papers by keyword
- arxiv/paper: get paper details by ID
- wikipedia/search: search articles with lang support
- wikipedia/summary: get article summary
Type safety fixes applied: wikiFetch returns unknown, typed search results.
Co-authored-by: BruceLoveDecimal <39156883+BruceLoveDecimal@users.noreply.github.com>