buildFullBackupPayload now asks every domain for its slice at once and
lays the slices out in the file's key order (backup-export-sections.ts),
merging the manifest where it first appears. The measurement, medication,
mood, instance-settings and nutrient readers and serialisers move out of
the payload builder into their domain modules; the records section keeps
its composition and manifest, while labs, illness, allergies, family
history, workouts and documents each export from their own module. The
measurement restore half moves to measurements-restore.ts so the export
graph does not pull in the restore's dependencies.
The file, its counts and their order are unchanged; the golden copies
still match. The measurement completeness guard now reads the domain
module and also checks that every carried column is written back.