displays: single display type with IP-driven role (dashboard/lobby/kiosk)

One 'display' image resolves what it shows from its own IP, like the existing
visitor-location BU mapping. Extend DashboardDefault with displayrole
(dashboard|lobby|partskiosk; migration 7d28, businessunitid now nullable since
only the dashboard role needs one) + a role->path map. New unauthenticated
GET /api/dashboarddefaults/display-role returns {role, path, businessunitid}
for the caller IP. Settings UI gains a Display selector, showing the business
unit only for the dashboard role.

shopdb/core/api/dashboarddefaults.py

@@ -9,6 +9,7 @@ from flask_jwt_extended import jwt_required
 
 from shopdb.extensions import db
 from shopdb.core.models import DashboardDefault, BusinessUnit, AuditLog
+from shopdb.core.models.dashboarddefault import DISPLAY_ROLES, DISPLAY_ROLE_PATHS
 from shopdb.utils.responses import success_response, error_response, ErrorCodes
 from shopdb.utils.authz import require_role
 
@@ -27,6 +28,7 @@ def _serialize(default):
     data = default.to_dict()
     data['businessunit'] = default.businessunit.businessunit \
         if default.businessunit else None
+    data['displaypath'] = default.displaypath
     return data
 
 
@@ -54,6 +56,35 @@ def visitor_location():
     })
 
 
+@dashboarddefaults_bp.route('/display-role', methods=['GET'])
+def display_role():
+    """Resolve what a single 'display' PC should show, from its own IP.
+
+    Unauthenticated: the display launcher calls this at boot. Returns the role
+    (dashboard / lobby / partskiosk), the frontend path it maps to, and the
+    business unit for the dashboard role. Unmapped IP -> null role.
+    """
+    ipaddress = request.args.get('ipaddress') or _request_ip()
+    default = DashboardDefault.query.filter_by(
+        ipaddress=ipaddress, isactive=True).first()
+    if not default:
+        return success_response({
+            'ipaddress': ipaddress,
+            'role': None,
+            'path': None,
+            'businessunitid': None,
+            'businessunit': None,
+        })
+    return success_response({
+        'ipaddress': ipaddress,
+        'role': default.displayrole,
+        'path': default.displaypath,
+        'businessunitid': default.businessunitid,
+        'businessunit': default.businessunit.businessunit
+        if default.businessunit else None,
+    })
+
+
 @dashboarddefaults_bp.route('', methods=['GET'])
 @jwt_required(optional=True)
 def list_defaults():
@@ -70,20 +101,30 @@ def create_default():
     """Create a visitor-IP -> business-unit mapping."""
     data = request.get_json() or {}
     ipaddress = (data.get('ipaddress') or '').strip()
+    role = (data.get('displayrole') or 'dashboard').strip()
     businessunitid = data.get('businessunitid')
 
     if not ipaddress:
         return error_response(ErrorCodes.VALIDATION_ERROR, 'ipaddress is required')
-    if not businessunitid:
-        return error_response(ErrorCodes.VALIDATION_ERROR, 'businessunitid is required')
-    if not db.session.get(BusinessUnit, businessunitid):
-        return error_response(ErrorCodes.NOT_FOUND, 'Business unit not found',
-                              http_code=404)
+    if role not in DISPLAY_ROLES:
+        return error_response(ErrorCodes.VALIDATION_ERROR,
+                              f'displayrole must be one of {", ".join(DISPLAY_ROLES)}')
+    # Only the dashboard role needs a business unit.
+    if role == 'dashboard':
+        if not businessunitid:
+            return error_response(ErrorCodes.VALIDATION_ERROR,
+                                  'businessunitid is required for the dashboard role')
+        if not db.session.get(BusinessUnit, businessunitid):
+            return error_response(ErrorCodes.NOT_FOUND, 'Business unit not found',
+                                  http_code=404)
+    else:
+        businessunitid = None
     if DashboardDefault.query.filter_by(ipaddress=ipaddress, isactive=True).first():
         return error_response(ErrorCodes.CONFLICT,
                               f"IP {ipaddress} is already mapped", http_code=409)
 
-    default = DashboardDefault(ipaddress=ipaddress, businessunitid=businessunitid,
+    default = DashboardDefault(ipaddress=ipaddress, displayrole=role,
+                               businessunitid=businessunitid,
                                description=data.get('description'))
     db.session.add(default)
     db.session.flush()
@@ -104,8 +145,14 @@ def update_default(default_id):
         return error_response(ErrorCodes.NOT_FOUND, 'Mapping not found', http_code=404)
 
     data = request.get_json() or {}
+    if 'displayrole' in data:
+        role = (data.get('displayrole') or '').strip()
+        if role not in DISPLAY_ROLES:
+            return error_response(ErrorCodes.VALIDATION_ERROR,
+                                  f'displayrole must be one of {", ".join(DISPLAY_ROLES)}')
+        default.displayrole = role
     if 'businessunitid' in data:
-        if not db.session.get(BusinessUnit, data['businessunitid']):
+        if data['businessunitid'] and not db.session.get(BusinessUnit, data['businessunitid']):
             return error_response(ErrorCodes.NOT_FOUND, 'Business unit not found',
                                   http_code=404)
         default.businessunitid = data['businessunitid']
@@ -114,6 +161,13 @@ def update_default(default_id):
     if 'description' in data:
         default.description = data['description']
 
+    # Non-dashboard roles carry no business unit; dashboard needs one.
+    if default.displayrole != 'dashboard':
+        default.businessunitid = None
+    elif not default.businessunitid:
+        return error_response(ErrorCodes.VALIDATION_ERROR,
+                              'businessunitid is required for the dashboard role')
+
     db.session.commit()
     return success_response(_serialize(default), message='Mapping updated')