Add photo management for models and employees; fix stale detail navigation

Model photos: upload/replace/delete on /api/models/<id>/image (admin),
stored under instance/modelimages/ with a public serve route; thumbnail
plus Upload/Replace/Remove controls in the Models settings modal; the
URL field remains as a manual alternative.

Employee photos, mode-aware: self-hosted directory employees get
upload/replace/delete (photo-<sso> under instance/employeephotos/,
employees plugin migration 0002); external directory mode passes the
HR-supplied picture URL through read-only (writes 409). One resolver
feeds both consumers - the shopfloor recognition/recert kiosk cards and
the employee detail hero - in either mode.

Navigation fix: router-view is keyed on route path, so following a
relationship link between two assets of the same type (machine ->
dualpath machine) reloads the page instead of showing stale content;
query-only URL changes still avoid a remount.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

shopdb/core/models/__init__.py

@@ -9,7 +9,7 @@ from .businessunit import BusinessUnit
 from .dashboarddefault import DashboardDefault
 from .location import Location, LocationType
 from .operatingsystem import OperatingSystem
-from .relationship import AssetRelationship, RelationshipType
+from .relationship import AssetRelationship, RelationshipType, RelationshipTypePropagation
 from .communication import Communication, CommunicationType
 from .user import User, Role, Permission
 from .application import Application, AppVersion
@@ -40,6 +40,7 @@ __all__ = [
     # Relationships
     'AssetRelationship',
     'RelationshipType',
+    'RelationshipTypePropagation',
     # Communication
     'Communication',
     'CommunicationType',