printedparts stage 2: models, real 0001 baseline, tables live

PrintedItem (catalog: code, name, image, cached quantityonhand,
per-item threshold, bin) and PrintedItemTransaction (the ledger:
signed quantity change attributed to a badge-resolved employee).
Both registered in PLUGIN_TABLE_OWNERS; 0001 is a post-cutover real
baseline. The migration-guard test learns the new expected head.
Routes are a placeholder ping until the next stage - the scaffold's
list route imported the deleted scaffold model, which surfaces as an
empty 'Migration error' because the alembic env imports the models
package.

tests/test_plugin_migrations.py

@@ -54,6 +54,8 @@ EXPECTED_HEAD_REVISION['machines'] = 'machines0002rename'
 EXPECTED_HEAD_REVISION['employees'] = 'employees0002photo'
 # usb drops the dead usbcheckouts.machineid column on top of its anchor.
 EXPECTED_HEAD_REVISION['usb'] = 'usb0002dropmachineid'
+# printedparts is post-cutover: its 0001 really creates its tables.
+EXPECTED_HEAD_REVISION['printedparts'] = 'printedparts0001baseline'
 # notifications indexes businessunitid on top of its anchor.
 EXPECTED_HEAD_REVISION['notifications'] = 'notifications0002buidx'