Restore PO catalog format; keep i18n strictly additive

An earlier i18n commit ran the .po files through polib, which stripped the
standard "#:" source-reference comments and reflowed every catalog (~30k lines
of churn) — breaking the attranslate-friendly format the project maintains.

Restore all .po/.pot to their upstream format and re-append only the new
message ids introduced this session (page layout options, the page-layout
tooltip, and "Saving…") as plain additive entries with empty msgstr. Diff
against origin is now insertions only.

Claude-Session: https://claude.ai/code/session_01UvJrFnhoMRWBhmcrrjH6EN

Author: bigbruno