Fix per-package target setting not being used

[jensens]

Summary

Fixes #53: Per-package target setting is now correctly used when constructing checkout paths

This PR fixes the bug where individual package target settings were ignored when determining the checkout path. The issue was that config.py line 103 was using the default-target variable instead of the package's individual target setting.

Changes

1. Failing Test (Commit ef5b4d3)

Added test_per_package_target_override() that demonstrates the bug:

• Tests package with default target
• Tests package with custom target setting
• Tests package with interpolated target (e.g., ${settings:docs-directory})

2. The Fix (Commit 733ecf2)

File: src/mxdev/config.py line 104

Changed from:

package.setdefault("path", os.path.join(target, name))

To:

package.setdefault("path", os.path.join(package["target"], name))

This ensures the path uses the package's actual target (either custom or default) instead of always using the default-target.

3. Cross-Platform Test Fix (Commit 5800927)

Updated test to use pathlib.Path().as_posix() for path comparison, which handles both Unix (/) and Windows (\) path separators correctly.

4. Documentation (Commits 733ecf2 + 5800927)

• Updated CHANGES.md with fix entry
• Added pathlib preference to CLAUDE.md code style guidelines

Results

✅ All 24 tests pass (14 config + 10 other test files)
✅ All CI checks pass on Ubuntu, Windows, macOS (Python 3.8-3.14)
✅ Packages with custom target settings are now checked out to correct directories
✅ Packages without custom target continue to use default-target
✅ Variable interpolation like ${settings:docs-directory} works correctly

Test Plan

# Run the new test
pytest tests/test_config.py::test_per_package_target_override -v

# Run all config tests
pytest tests/test_config.py -v

# Verify linting
uvx --with tox-uv tox -e lint

Example Usage

[settings]
default-target = sources
docs-directory = documentation

[package-a]
url = https://github.com/example/package-a.git
# No target specified - uses default-target
# Checked out to: sources/package-a

[package-b]
url = https://github.com/example/package-b.git
target = custom-dir
# Checked out to: custom-dir/package-b

[documentation]
url = https://github.com/example/docs.git
target = ${settings:docs-directory}
# Checked out to: documentation/documentation