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.

plugins/printedparts/migrations/env.py

@@ -0,0 +1,14 @@
+"""Alembic environment for the printedparts plugin migration chain.
+
+Delegates to the shared runner in shopdb.plugins.alembic_template, which
+filters the metadata to this plugin's tables and drives Alembic against the
+per-plugin version table alembic_version_printedparts (ADR-008). This plugin
+is NEW (post-cutover): its 0001 baseline really CREATES its tables.
+"""
+import os
+
+os.environ['PLUGIN_NAME'] = 'printedparts'
+
+from shopdb.plugins.alembic_template import run_migrations  # noqa: E402
+
+run_migrations()