Build and behave correctly on every release target

Split platform into a portable core (mod.rs) plus unix.rs and windows.rs.

- Linux: statx through syscall(2) so static musl links (fstatat fallback
  on ENOSYS); virtual-fs detection compares f_type as u32.
- macOS: Finder trash (~/.Trash or /Volumes/X/.Trashes/<uid>, "name N"
  collisions, EXDEV falls through to the next location) and `open -R`
  reveal; never headless.
- FreeBSD/NetBSD: fstatat with birth time; trash and reveal unsupported,
  permanent delete still available on headless systems.
- Windows: std read_dir and metadata, allocated size unknown, no inode
  identity, Recycle Bin via SHFileOperationW (FOF_ALLOWUNDO, all
  architectures), Explorer /select reveal, no permanent delete, '\\'
  separator with Windows glob semantics, abs paths via GetFullPathNameW,
  config in %AppData%.
- Local time via a portable LocalTime helper (localtime_r tm_gmtoff on
  Unix, SystemTimeToTzSpecificLocalTime on Windows) replacing libc tm and
  mktime in the TUI, snapshot and filter code.
- errno, stat field names and mode_t width handled per OS; Unix-only
  tests gated; clippy clean on all targets.

Adds windows-sys =0.61.2 (Windows only; Win32_Foundation,
Win32_System_Time, Win32_UI_Shell), already in the lockfile via crossterm.

Cargo.lock

@@ -194,6 +194,7 @@ dependencies = [
  "sha2",
  "unicode-segmentation",
  "unicode-width",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]