fix(manager): parse file labels across platforms

[kmnhan]

Summary

• Parse recorded file stems with pathlib.PureWindowsPath so manager labels accept Windows, UNC, and POSIX path syntax on all operating systems.
• Use the same parser for live manager rows and restored workspace labels.
• Keep each recorded source path unchanged for replay, diagnostics, and file relinking.

Root cause

pathlib.Path.stem uses the current operating system's path rules. On macOS, it treats backslashes in a recorded Windows path as ordinary filename characters. The manager therefore displayed most of the Windows path instead of only the file stem.

User impact

ImageTool workspaces moved from Windows to macOS now show compact source filenames in the manager tree.

Validation

• QT_QPA_PLATFORM=offscreen uv run --group pyqt6 pytest -q tests/interactive/imagetool/manager/provenance/test_dependencies.py::test_manager_compact_file_suffix tests/interactive/imagetool/manager/provenance/test_dependencies.py::test_manager_compact_file_suffix_accepts_cross_platform_paths tests/interactive/imagetool/manager/workspace/test_format.py (23 passed)
• uv run --group pyqt6 ruff format --check on all changed files
• uv run --group pyqt6 ruff check on all changed files
• uv run --group pyqt6 mypy on all changed source files
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.65%. Comparing base (08e0b56) to head (193fce3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #516   +/-   ##
=======================================
  Coverage   91.65%   91.65%           
=======================================
  Files         247      247           
  Lines       94768    94770    +2     
  Branches    15881    15881           
=======================================
+ Hits        86858    86862    +4     
+ Misses       4593     4591    -2     
  Partials     3317     3317           

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