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/extensions.py

@@ -0,0 +1,28 @@
+"""Flask extensions initialization."""
+
+from flask_sqlalchemy import SQLAlchemy
+from flask_migrate import Migrate
+from flask_jwt_extended import JWTManager
+from flask_cors import CORS
+from flask_marshmallow import Marshmallow
+from flask_caching import Cache
+
+# Initialize extensions without app
+db = SQLAlchemy()
+migrate = Migrate()
+jwt = JWTManager()
+cors = CORS()
+ma = Marshmallow()
+cache = Cache()
+
+
+def init_extensions(app):
+    """Initialize all Flask extensions with app."""
+    db.init_app(app)
+    migrate.init_app(app, db)
+    jwt.init_app(app)
+    cors.init_app(app, resources={
+        r"/api/*": {"origins": app.config.get('CORS_ORIGINS', '*')}
+    })
+    ma.init_app(app)
+    cache.init_app(app)