`chezmoi apply` on Linux printed "could not regenerate kitty theme
files" every run. GNU stat reads -f as --file-system, so
`stat -f '%Lp' file` prints a block of filesystem info to stdout and
exits non-zero. The `|| stat -c '%a'` fallback then appended the real
answer to that block, and chmod rejected the result, failing the script
under set -e.
Replace the chain with a file_mode() helper in both scripts: try the GNU
form first, since BSD rejects -c cleanly without printing anything, and
accept the answer only if it is octal. Covered by a new case in
tests/test_theme_mode.sh using a stat stub that reproduces GNU's
behaviour; it fails against the old chain.
a84778a640