- absolutePath() no longer routes through SystemFileSystem.resolve, which
  threw FileNotFoundException for relative paths of files that do not exist.
  This broke `write`/`copyTo` on any relative destination, since
  isSameLogicalFileAs() calls absolutePath() before the file is created.
  It now resolves against getcwd(), matching JVM and Windows native.
- mimeType() returned null unconditionally. It now reads the freedesktop.org
  shared-mime-info database, falling back to /etc/mime.types, cached lazily.
- Fix ktlint violations that were failing the CI lint job (import ordering,
  argument list wrapping, max line length, consecutive blank lines).
- Drop redundant .toLong() conversions on st_ctim/st_mtim and the unused
  withContext import; document why st_ctim is used for createdAt().
- Honour the XDG Base Directory rule that XDG_* variables are ignored unless
  they hold an absolute path.
- Replace findByName("linuxMain")?.dependsOn(...) with linuxMain.get() so a
  missing source set fails loudly instead of silently skipping desktopMain.
- Add a linuxX64Test CI job so the new targets are actually exercised, plus
  Linux specific absolutePath() regression tests.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

…tests

Rebased onto main (80b901d), which added two expect declarations in vinceglb#625 that
Linux had no actual for, so the merge no longer compiled:
- withPath() in jvmAndNativeMain
- resolveBookmarkData() in nonWebMain, replacing the old fromBookmarkData shape
Both are now implemented, mirroring mingwX64.

createdAt() no longer reports st_ctim. That is the inode status change time and
is updated by writes and chmod, so it was reporting a fabricated creation time.
Linux only exposes birth time via statx(STATX_BTIME), which Kotlin/Native does
not bind and which several filesystems do not support, so null is returned.
See https://man7.org/linux/man-pages/man7/inode.7.html

MIME lookup now honours the globs2 `cs` flag, so case sensitive entries such as
`*.C:cs` (C++ source) no longer collide with `*.c` (C source). Compound globs
like `*.tar.gz` stay excluded on purpose: `extension` is the segment after the
last dot, so registering them under "gz" would shadow the correct entry.

filesDir/cacheDir no longer fall back to relative `.local/share` and `.cache`
when HOME is unset, which could plant application data in the working
directory. The passwd database is consulted first and a FileKitException is
thrown if no absolute home can be resolved.

Also:
- Make the globs2 and mime.types parsers pure functions over their content so
  the matching rules are unit testable rather than host dependent.
- Collapse the two duplicated FileKitUserDirectory switches into extension
  properties so XDG keys and folder names cannot drift.
- Expand linuxTest to 25 tests covering timestamps, bookmarks, MIME matching,
  FileKit initialization and directory resolution; rename to the documented
  Subject_action_expectation convention.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>