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/templates/parks/partials/park_header_badge.html

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+{# Park header status badge partial - refreshes via HTMX on park-status-changed #}
+<span id="park-header-badge"
+      hx-get="{% url 'parks:park_header_badge' park.slug %}"
+      hx-trigger="park-status-changed from:body"
+      hx-swap="outerHTML">
+{% if perms.parks.change_park %}
+    <!-- Clickable status badge for moderators -->
+    <button type="button"
+            onclick="document.getElementById('park-status-section').scrollIntoView({behavior: 'smooth'})"
+            class="status-badge text-sm font-medium py-1 px-3 transition-all hover:ring-2 hover:ring-blue-500 cursor-pointer
+                   {% if park.status == 'OPERATING' %}status-operating
+                   {% elif park.status == 'CLOSED_TEMP' or park.status == 'CLOSED_PERM' %}status-closed
+                   {% elif park.status == 'UNDER_CONSTRUCTION' %}status-construction
+                   {% elif park.status == 'DEMOLISHED' %}status-demolished
+                   {% elif park.status == 'RELOCATED' %}status-relocated{% endif %}">
+        {{ park.get_status_display }}
+        <i class="fas fa-chevron-down ml-1 text-xs"></i>
+    </button>
+{% else %}
+    <!-- Static status badge for non-moderators -->
+    <span class="status-badge text-sm font-medium py-1 px-3
+                 {% if park.status == 'OPERATING' %}status-operating
+                 {% elif park.status == 'CLOSED_TEMP' or park.status == 'CLOSED_PERM' %}status-closed
+                 {% elif park.status == 'UNDER_CONSTRUCTION' %}status-construction
+                 {% elif park.status == 'DEMOLISHED' %}status-demolished
+                 {% elif park.status == 'RELOCATED' %}status-relocated{% endif %}">
+        {{ park.get_status_display }}
+    </span>
+{% endif %}
+</span>

backend/templates/parks/partials/park_history.html

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+{% comment %}
+Park FSM History Partial Template
+
+Displays FSM transition history for a specific park.
+Loaded via HTMX when the history section is expanded.
+
+Required context:
+  - park: The Park model instance
+{% endcomment %}
+
+<div class="mt-4">
+    <div id="park-history-container"
+         hx-get="{% url 'moderation:moderation-reports-all-history' %}?model_type=park&object_id={{ park.id }}"
+         hx-trigger="load"
+         hx-swap="innerHTML"
+         hx-indicator="#park-history-loading">
+        <!-- Loading State -->
+        <div id="park-history-loading" class="flex items-center justify-center py-8">
+            <i class="mr-2 text-blue-500 fas fa-spinner fa-spin"></i>
+            <span class="text-gray-600 dark:text-gray-400">Loading history...</span>
+        </div>
+    </div>
+</div>

backend/templates/parks/partials/park_status_actions.html

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+{% load fsm_tags %}
+
+{# This partial is loaded via HTMX into #park-status-section. It must include the container #}
+{# element with the same id and hx-* attributes to preserve targeting for subsequent transitions. #}
+<div id="park-status-section"
+     data-park-status-actions
+     hx-get="{% url 'parks:park_status_actions' park.slug %}"
+     hx-trigger="park-status-changed from:body"
+     hx-swap="outerHTML">
+{% if user.is_authenticated and perms.parks.change_park %}
+<div class="mb-6 p-4 bg-blue-50 dark:bg-blue-900/20 border border-blue-200 dark:border-blue-800 rounded-lg">
+    <h3 class="text-sm font-semibold text-blue-900 dark:text-blue-100 mb-3">
+        <i class="fas fa-cog mr-2"></i>Status Management
+    </h3>
+
+    {% include "htmx/status_with_actions.html" with object=park user=user target_id="park-status-section" %}
+</div>
+{% endif %}
+</div>