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/core/models/businessunit.py

@@ -0,0 +1,31 @@
+"""Business Unit model."""
+
+from shopdb.extensions import db
+from .base import BaseModel
+
+
+class BusinessUnit(BaseModel):
+    """Business unit / department model."""
+    __tablename__ = 'businessunits'
+
+    businessunitid = db.Column(db.Integer, primary_key=True)
+    businessunit = db.Column(db.String(100), unique=True, nullable=False)
+    code = db.Column(db.String(20), unique=True, comment='Short code')
+    description = db.Column(db.Text)
+
+    # Optional parent for hierarchy
+    parentid = db.Column(
+        db.Integer,
+        db.ForeignKey('businessunits.businessunitid'),
+        nullable=True
+    )
+
+    # Self-referential relationship for hierarchy
+    parent = db.relationship(
+        'BusinessUnit',
+        remote_side=[businessunitid],
+        backref='children'
+    )
+
+    def __repr__(self):
+        return f"<BusinessUnit {self.businessunit}>"