[BUG] test_persist_current_sets_0600_mode fails on Windows - Unix file permissions not supported

[Taha-KT]

Environment:

• OS: Windows 10/11
• Python: 3.13.11
• Strix version: main branch (latest)

Steps to reproduce:

1. Clone repo on Windows
2. Run uv sync
3. Run uv run pytest tests/test_config_loader.py::test_persist_current_sets_0600_mode

Expected: Test passes or is skipped on Windows.

Actual:

Windows st_mode returns 33206 (regular file), not 0o600 (Unix permission). Unix file permissions don't exist on Windows.

Suggested fix: Skip this test on Windows (os.name == 'nt') or use stat.S_IMODE() with a platform check.

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Additional context:
I am setting up Strix for local development on Windows and encountered this during uv run pytest. The persist_current() method in strix/config/loader.py sets 0o600 mode, but Windows doesn't support Unix-style file permissions. This blocks Windows contributors from running the full test suite cleanly.

[Taha-KT]

I'd like to work on this fix. I can reproduce it consistently on Windows.