Closes # (none)

## Summary

Improved the jump-to-definition reliability for file paths in prose
strings (comments, markdown, etc.) by smarter stripping of surrounding
punctuation.

This allows `cmd/ctrl-click` to work on file paths in contexts like:
- **Markdown backticks**: `` `path/to/file` ``
- **Markdown links**: `[link](path/to/file)`
- **Parentheses**: `(see path/to/file)`
- **Sentence endings**: `Check path/to/file.`
- **Code spans**: `` `cat path/to/file` ``

## Technical Details

- Updated `link_pattern_file_candidates` in `hover_links.rs` to
iteratively trim common leading and trailing punctuation characters.
- Candidate generation now produces multiple variations (trimmed, regex
match, raw) ordered by specificity (most trimmed first).
- Refactored `test_hover_filenames` to be DRY: it now uses a single base
document string and targeted replacements, making it easier to add new
prose test cases without duplication.

Release Notes:

- Improved jump-to-definition reliability for file paths wrapped in
punctuation (backticks, parens, sentence endings).

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Co-authored-by: Martin Ye <martin@zed.dev>
Co-authored-by: MartinYe1234 <52641447+MartinYe1234@users.noreply.github.com>