Support angle bracket syntax for links to files with spaces

[Copilot]

GitHub UI uses angle bracket syntax [text](<file name.md>) for links with spaces, but the plugin failed to match these against actual files, breaking links on GitHub Pages.

Changes

• Added strip_angle_brackets method to remove wrapping angle brackets from link paths before processing
• Updated link_parts to apply stripping to captured paths from both inline and reference-style links
• Added test coverage for raw spaces, angle bracket syntax, and URL-encoded combinations

Supported formats

All now convert to proper Jekyll URLs (/file%20name.html):

[link](page with space.md)           # Raw spaces
[link](<page with space.md>)         # Angle brackets (now fixed)
[link](page%20with%20space.md)       # URL-encoded
[ref]: <page with space.md>          # Reference style (now fixed)

The fix uses regex \A<(.+)>\z with anchors to safely strip only fully-wrapped paths.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Adding links to .md with space in the name</issue_title>
<issue_description>I've tried several strategies, but none truely works.
Here is the repo/file that demonstrates the issue: https://github.com/EugeneLoy/ghp-test/blob/main/README.md
Url to Github pages of this repo is: https://eugeneloy.github.io/ghp-test/

[1] works fine, since there is no space in filename.
[2] works on Github pages url, but does not work in Github UI, since it does not adhere to GFM (I guess).
[3] - [7] all fail to work on Github pages url (some of them work in Github UI though).

I am not sure whether this behavior is a bug or what I want can be classified as feature request, but I would like to know how to achieve links to .md files with spaces in filenames that work both in Github UI and on Github pages. If there are some workarounds that can achieve this - I would also like to know.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Adding links to .md with space in the name #102

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