Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 2
src/chevah_compat/unix_filesystem.py:222-224
**Unreachable legacy root check**

The `if path == '/'` guard (line 224) is now dead code. `_rejectRoot` at the top of this method calls `isRoot`, which already raises `CompatError(1009, ...)` before execution reaches the old check. The two checks also emit different error messages, which could be confusing during debugging if the legacy block were ever reachable.

### Issue 2 of 2
src/chevah_compat/posix_filesystem.py:390-396
**Case-insensitive comparison applied to POSIX paths**

`isRoot` uses `.lower()` on both paths unconditionally. On case-sensitive POSIX filesystems (Linux ext4, etc.), a virtual root configured as `/Home/sftp_root` and a path `/home/sftp_root` would be considered equal, incorrectly blocking operations on the distinct lowercase path. Consider limiting the case-insensitive fold to Windows only, or using `os.path.normcase` which already applies `.lower()` on Windows and is a no-op on POSIX.

```suggestion
        return os.path.normcase(root) == os.path.normcase(path)
```

### Issue 1
src/chevah_compat/tests/normal/test_filesystem.py:34-42
**NT unlocked filesystem: `['..']` and `['child', '..']` raise `OSError`, not `CompatError`**

On the NT unlocked filesystem (`lock_in_home_folder = False`), `getRealPathFromSegments` interprets the first segment as a drive letter. Passing `['..']` produces `drive = '..\\'`, which fails `_validateDrivePath` with `OSError(EINVAL)` — well before `_rejectRoot` can raise `CompatError(1009)`. The same happens for `['child', '..']` because `'child'` is not a single-letter drive. `assertRaises(CompatError, …)` does not catch `OSError`, so `test_deleteFolder_root` in `TestLocalFilesystemUnlocked` will fail on Windows for those two segment forms. The locked filesystem is not affected because `_getLockedPathFromSegments` collapses `['..']` back to `root_path` before any drive validation.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.