## Summary

- Open relative file links with GitHub-style line fragments at the
referenced line
- Support line navigation from agent responses and Markdown previews
- Preserve decoded-first path resolution with literal percent-escape
fallback

## Testing

- cargo test -q -p util test_source_line_from_fragment -- --nocapture
- cargo test -q -p acp_thread test_hyperlink_percent_escapes_are_decoded
-- --nocapture
- cargo test -q -p agent_ui test_open_link -- --nocapture
- cargo test -q -p markdown_preview -- --nocapture
- cargo fmt --all -- --check

Release Notes:

- Improved relative file links with line numbers to open at the
referenced line.