Initial import: shopdb-flask multi-site asset platform

Flask + Vue rewrite of the classic-ASP shopdb, built as a plugin
framework so sister GE Aerospace sites can adopt it. Product version
0.7.0-pre-0.8.0, plugin contract 0.11.0, 966 backend tests.

Key entry points:
- docs/INSTALL-WINDOWS-IIS.md - tested Windows + IIS install runbook
  (own-site and subpath deployment methods)
- docs/PILOT-DEPLOY.md - production pilot: stand up + import + verify
- docs/IMPORT-API.md - schema-agnostic legacy data import contract
- scripts/site_imports/wjf/ - West Jefferson reference import loader
- docs/adr/ - twelve accepted architecture decision records

shopdb/plugins/templates/schemas/__init__.py.tmpl

@@ -0,0 +1,6 @@
+"""$Name plugin schemas (marshmallow).
+
+Add schema classes here when you need request/response validation
+beyond the simple to_dict() output. The framework wires marshmallow
+into the response helpers; see the PLUGIN-HOOKS wiki page for details.
+"""