luks-slots --owner: exit 4 when no owner slot is recorded

[maralcbr]

This applies the final luks-slots --owner contract agreed with the upstream runtime work (omacom#13362). It follows #659.

• Exit 0: prints the owner slot, which is recorded and present in the LUKS header.
• Exit 4: only when nothing is recorded, meaning encrypt.state is missing or has no owner_slot entry. Stderr starts "No owner key slot is recorded".
• Exit 1 with the reason on stderr for everything else: an empty or non-numeric record, a slot absent from the header, an unreadable header or encrypt.state, the crypttab device not found, not Apple Silicon, or the Boot partition not mounted.
• Never exit 2 or 3: the dispatcher uses those.

Release order: this omarchy-mac-boot must publish with or before the runtime that interprets exit 4. Noted on omacom/omarchy-pkgs#673.

Tested in an Arch container: packages/omarchy-mac/boot/test/all passes. The --owner tests now check each exit code:

• 4 for a missing file and for a missing entry, and that stderr leads with the no-record message
• 1 for an empty value, a non-numeric value, a value out of range, a slot absent from the header, a token standing in for a slot, an unreadable header, a missing crypttab device, another platform and an unmounted Boot partition
• no file changed in any case