Add the printedparts plugin: 3D-printed parts storefront and kiosk

Catalog with photos and append-only print-file revisions, a stock
ledger attributing every take/restock/adjust to a badge-resolved
employee, a touch kiosk (scan bin, scan badge, keypad quantity) with a
deliberately open decrement-only take endpoint, 1x0.5in CODE128 bin
labels, low-stock email alerts to selected users, roles, or addresses,
and stock/consumption/by-person reports with a cache-vs-ledger
reconcile. Ships disabled; enable per site. Contract 0.13.0 adds the
mailer and the User/Role models to the plugin surface.

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()