[patch] Fix crash navigating to the parent directory in the filesystem browser

[matt-edmondson]

Fixes #281.

Problem

Double-clicking .. in the filesystem browser crashed on Linux:

System.ArgumentException: Cannot convert "home" to AbsoluteDirectoryPath
   at ktsu.Semantics.Strings.SemanticString`1.PerformValidation[TDest](TDest value)
   at ktsu.ImGui.Popups.ImGuiPopups.FilesystemBrowser.DrawFileTable()

The handler took the parent by trimming directory separators off the path string:

Path.GetDirectoryName(CurrentDirectory.WeakString.Trim(Path.DirectorySeparatorChar))

Trim strips separators from both ends. On Unix the leading / is the root, so /home/lsma became home/lsma, whose parent home is relative and fails AbsoluteDirectoryPath validation. Windows drive paths start with C:\ rather than a separator, which is why only Linux saw it — but UNC paths (\server\share\…) hit the identical bug on Windows, and that reproduced locally as Cannot convert "server\share\folder" to AbsoluteDirectoryPath.

A second, quieter bug came from the same line: going up from /home produced an empty path, so the browser silently showed no contents instead of landing on /.

Change

Take the parent from the path type instead of doing string math:

CurrentDirectory = CurrentDirectory.Parent;
RefreshContents();

No guard is needed because ktsu-dev/Semantics#144 made a root its own parent, so .. simply stays put once there is nowhere left to go. That shipped as ktsu.Semantics 2.9.0, which this PR bumps to (all four ktsu.Semantics.* packages together — one repo, one version).

The root-cause fix living in Semantics is why there is no ParentOf helper here and no regression test in this repo: the behaviour under test is AbsoluteDirectoryPath.Parent, and it is covered by 7 new tests in Semantics.Test/Paths/AbsoluteDirectoryPathParentTests.cs (parent chains, root-is-its-own-parent, UNC share roots, never returning an empty or relative path while walking up, termination at the fixed point, GetAncestors behaviour), written so the Unix cases execute on Linux CI rather than skipping.

Verification

• dotnet build ImGui.sln against 2.9.0: clean, 0 warnings (warnings-as-errors, so the Semantics behaviour change introduced no new diagnostics).
• dotnet test ImGui.sln: 604 total, 0 failed, 8 OS-skipped.
• Ran the .. walk on real Linux (WSL) against ktsu.Semantics.Paths 2.9.0 from nuget.org, no patched binaries: /home/matt/parenttest → /home/matt → /home → /, then stays at /. The exact exception from the issue no longer occurs.
• Semantics side: full suite 1079 passed, 0 failed.

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

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