#364 feat: add --sort to research search-papers and print row dates

firecrawl research search-papers takes --sort relevance|date_desc, prints each row's created and updated dates, and reads row authors as a name list.

firecrawl research search-papers "speculative decoding" --sort date_desc

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Summary by cubic

firecrawl research search-papers now takes --sort relevance|date_desc and prints each paper row's created and updated dates.

• Sends the sort value on both the API-key and keyless paths.
• Renders authors as names, capped at 15, with et al. for name lists and +N more for comma-joined strings.
• Documents --sort in README.md and --sort, --from, and --to in the firecrawl-research-index skill.