Review feedback on #2879: a locale file with no counterpart in `agents/` was
skipped, so every other case here silently passed over it. Retiring an agent
would leave its seven translations behind with nothing to compare against and
nothing to report it.
Collect those files while building the list and assert the collection is empty.
Zero today across 199 locale docs, so this changes no current result; planting
one orphan takes the file to `Passed: 6, Failed: 1` and exit 1.
Nguyen Thanh Dat
4f18d1eb87