Preserve remotes when publishing database changes

[pH-7]

The publishing helper currently removes and recreates origin for every mirror. It now preserves remote configuration, explicitly pushes the checked-out branch, rejects dirty/detached checkouts and stops at the first failed push. Optional destination arguments support publishing only to a verified remote; historical defaults remain available.

The README records the June 2019 export's import blockers and explains the current helper. All 815 SQL chunks and the ODbL licence remain unchanged. The export has 818,846 INSERT statements; a read-only barcode count finds 70 duplicated barcodes. Missing nutrition values and duplicate-record policy need a separate data migration decision.

Validation:

• Five offline publishing-helper regressions pass, including quoted destinations, preserved remote configuration, default order, dirty/detached rejection and failure propagation.
• Bash syntax, critical Python lint and Git whitespace checks pass.
• Disposable MySQL 8.4.11 strict import fails on a blank dietary_fiber value in the first chunk. A separate diagnostic permissive import fails on duplicate barcode 0019320001376. These reproduce existing data limitations; no real database was modified.

This draft does not assert that the SQL snapshot is ready for a production import.