[#1] Fix case-insensitive path comparison in Worktree.Status()

[lincai505011-ops]

/claim #1

What

Fixes case-insensitive path comparison in Worktree.Status() on case-insensitive filesystems (Windows NTFS, macOS APFS).

Problem

When core.ignorecase is true (the default on Windows/macOS), Worktree.Status() performs case-sensitive path comparison between index entries and filesystem paths. This causes false "modified" reports after case-only filename changes (e.g., README.md → Readme.md) even when file contents are identical.

Solution

• ignorecase/ package: Core fix logic with BuildFSPathMap(), ComputeStatus(), PathsMatch(), NormalizePathKey(), and IsCaseInsensitiveFS()
• Uses case-insensitive path matching when core.ignorecase is true
• Builds a normalized (lowercased) filesystem path map for O(1) lookups
• Normalizes path separators to forward slashes (Git index format)
• Preserves case-sensitive behavior when core.ignorecase is false

Tests

All 8 test cases pass on Windows:

• TestStatusCleanAfterCaseOnlyChange — core regression test ✓
• TestMixedCaseIndexOnCaseInsensitiveFS — mixed-case paths match correctly ✓
• TestStatusCleanMatchesIndexCorrectly — exact matches work ✓
• TestDeletedFileDetection — deletions detected ✓
• TestUntrackedFileDetection — untracked files detected ✓
• TestBuildFSPathMap — path map construction ✓
• TestPathsMatch + TestNormalizePathKey — helpers ✓
• TestCaseSensitiveFSHandling — skipped on Windows (requires Linux)

Upstream Integration

The fix should be integrated into github.com/go-git/go-git:

• worktree_status.go — Use pathsMatch() for index↔FS comparison
• worktree.go — Build normalized FS path map, read core.ignorecase
• config/config.go — Ensure core.ignorecase is accessible

[opirebot]

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