Fix Firefox bookmark profile resolution for LF-formatted profiles.ini

[Copilot]

Firefox 155 can rewrite profiles.ini with LF line endings, which broke the Browser Bookmarks loader’s CRLF-only parsing and caused Firefox bookmarks to disappear silently. This change makes profile parsing line-ending agnostic and adds regression coverage.

• Loader fix: line-ending agnostic profiles.ini parsing

  • Replaced manual "\r\n" splitting with File.ReadAllLines(...) in FirefoxBookmarkLoader.GetProfileIniPath.
  • Preserves existing profile-selection logic while correctly handling both CRLF and LF files.

• Regression test coverage

  • Added BrowserBookmarkPluginTest.GetProfileIniPath_ParsesDefaultProfileWithDifferentLineEndings.
  • Verifies default profile resolution for both \n and \r\n profiles.ini content.

• Test project wiring

  • Added Browser Bookmark plugin project reference to Flow.Launcher.Test so the regression test can target the loader.

// before
var lines = ini.Split("\r\n").ToList();

// after
var lines = File.ReadAllLines(profileIni).ToList();

• Fixes BUG: Browser Bookmarks: Firefox bookmarks disappear when profiles.ini uses LF line endings (Firefox 155) #4642