fix: tavily response_time type, rewrite jina backend to use POST JSON…

… API

- Fix tavily: response_time field changed from string to float64 to match API
- Rewrite jina backend per official docs: POST with JSON body instead of GET
- Use proper request fields (q, hl) and X-Site header for site filtering
- Parse structured JSON response (data[] array) instead of markdown links
- Pass language option through to jina hl parameter

feat: add exa and jina backends with mcp and api support

fix: rename AUR packages to sx-search/sx-search-bin (sx is taken)

Initial commit