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/customfield.py

@@ -0,0 +1,94 @@
+"""Custom fields: site-defined extra attributes per asset type.
+
+A CustomField is a definition scoped to one asset type (machine, computer,
+printer, network_device). A CustomFieldValue holds one asset's value for one
+field. This is the generic form of the built-in identifier columns - sites add
+their own attributes without a schema change.
+"""
+
+from shopdb.extensions import db
+
+# Allowed datatypes for a custom field. Values are always stored as text and
+# cast on render/input by the frontend.
+CUSTOM_FIELD_DATATYPES = ('text', 'number', 'date', 'boolean', 'select')
+
+
+class CustomField(db.Model):
+    __tablename__ = 'customfields'
+
+    fieldid = db.Column(db.Integer, primary_key=True)
+    assettypeid = db.Column(
+        db.Integer,
+        db.ForeignKey('assettypes.assettypeid'),
+        nullable=False,
+        comment='Which asset category this field applies to'
+    )
+    # Machine-name key, unique per asset type. Used for stable references.
+    fieldkey = db.Column(db.String(50), nullable=False)
+    label = db.Column(db.String(150), nullable=False)
+    datatype = db.Column(db.String(20), nullable=False, server_default='text')
+    # JSON array of options, only meaningful when datatype='select'
+    options = db.Column(db.Text)
+    showondetail = db.Column(db.Boolean, nullable=False, server_default='1')
+    showonform = db.Column(db.Boolean, nullable=False, server_default='1')
+    sortorder = db.Column(db.Integer, nullable=False, server_default='0')
+    isactive = db.Column(db.Boolean, nullable=False, server_default='1')
+    # When true, this field's values are matched by global search.
+    searchable = db.Column(db.Boolean, nullable=False, server_default='0')
+
+    __table_args__ = (
+        db.UniqueConstraint('assettypeid', 'fieldkey', name='uq_customfield_type_key'),
+    )
+
+    def to_dict(self):
+        import json
+        parsed_options = []
+        if self.options:
+            try:
+                parsed_options = json.loads(self.options)
+            except (ValueError, TypeError):
+                parsed_options = []
+        return {
+            'fieldid': self.fieldid,
+            'assettypeid': self.assettypeid,
+            'fieldkey': self.fieldkey,
+            'label': self.label,
+            'datatype': self.datatype,
+            'options': parsed_options,
+            'showondetail': bool(self.showondetail),
+            'showonform': bool(self.showonform),
+            'sortorder': self.sortorder,
+            'isactive': bool(self.isactive),
+            'searchable': bool(self.searchable),
+        }
+
+
+class CustomFieldValue(db.Model):
+    __tablename__ = 'customfieldvalues'
+
+    valueid = db.Column(db.Integer, primary_key=True)
+    fieldid = db.Column(
+        db.Integer,
+        db.ForeignKey('customfields.fieldid', ondelete='CASCADE'),
+        nullable=False
+    )
+    assetid = db.Column(
+        db.Integer,
+        db.ForeignKey('assets.assetid', ondelete='CASCADE'),
+        nullable=False
+    )
+    value = db.Column(db.Text)
+
+    field = db.relationship('CustomField')
+
+    __table_args__ = (
+        db.UniqueConstraint('fieldid', 'assetid', name='uq_customfieldvalue_field_asset'),
+    )
+
+    def to_dict(self):
+        return {
+            'valueid': self.valueid,
+            'fieldid': self.fieldid,
+            'assetid': self.assetid,
+            'value': self.value,
+        }