Add test utilities and state machine diagrams for FSM models

- Introduced reusable test utilities in `backend/tests/utils` for FSM transitions, HTMX interactions, and common scenarios.
- Added factory functions for creating test submissions, parks, rides, and photo submissions.
- Implemented assertion helpers for verifying state changes, toast notifications, and transition logs.
- Created comprehensive state machine diagrams for all FSM-enabled models in `docs/STATE_DIAGRAMS.md`, detailing states, transitions, and guard conditions.

backend/apps/rides/urls.py

@@ -1,5 +1,6 @@
 from django.urls import path
 from . import views
+from apps.core.views.views import FSMTransitionView
 
 app_name = "rides"
 
@@ -83,4 +84,12 @@ urlpatterns = [
         views.RideUpdateView.as_view(),
         name="ride_update",
     ),
+    # FSM transition endpoint for rides
+    # URL: /rides/<ride_slug>/transition/<transition_name>/
+    path(
+        "<slug:slug>/transition/<str:transition_name>/",
+        FSMTransitionView.as_view(),
+        {"app_label": "rides", "model_name": "ride"},
+        name="ride_transition",
+    ),
 ]