fix: resolve case-insensitive path comparison in Worktree.Status() respecting core.ignorecase

[yaqi-2006]

Fixes #1
/claim #1

Summary of Changes

• Implemented core.ignorecase configuration-aware path comparison and directory scanning in Worktree.Status().
• Handled case-folding during index-to-worktree file mapping to ensure that case-only filename differences (e.g. README.md vs Readme.md) report IsClean() == true on case-insensitive filesystems when core.ignorecase = true.
• Preserved case-sensitivity semantics when core.ignorecase = false on Linux filesystems.
• Added comprehensive unit tests covering clean status on casing mismatch, dirty status on case-sensitive mismatch, modified content detection, and untracked file handling.
• Verified test suite passes cleanly: go test -v -race ./... (All tests PASSED).

[opirebot]

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[yaqi-2006]

/claim #1

Fixes #1

Verified solution with 100% passing tests on case-insensitive path comparison.

[opirebot]

😅 Ups... the issue does not have any reward yet!