feat: fix test collection and add collection stats display

- Fix collect_tests to use JSON report parsing (was returning 0 tests)
- Add Test Collection panel to testing dashboard showing total tests,
  unit/integration/performance breakdown, and file count
- Reorganize sidebar: create Platform Health section with Testing Hub,
  Code Quality, and Background Tasks
- Keep Developer Tools for Components and Icons only
- Platform Monitoring now contains Import Jobs and Application Logs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/admin/partials/sidebar.html

@@ -96,14 +96,19 @@
     {% call section_content('devTools') %}
         {{ menu_item('components', '/admin/components', 'view-grid', 'Components') }}
         {{ menu_item('icons', '/admin/icons', 'photograph', 'Icons') }}
+    {% endcall %}
+
+    <!-- Platform Health Section -->
+    {{ section_header('Platform Health', 'platformHealth') }}
+    {% call section_content('platformHealth') %}
         {{ menu_item('testing', '/admin/testing', 'beaker', 'Testing Hub') }}
         {{ menu_item('code-quality', '/admin/code-quality', 'shield-check', 'Code Quality') }}
+        {{ menu_item('background-tasks', '/admin/background-tasks', 'collection', 'Background Tasks') }}
     {% endcall %}
 
     <!-- Platform Monitoring Section -->
     {{ section_header('Platform Monitoring', 'monitoring') }}
     {% call section_content('monitoring') %}
-        {{ menu_item('background-tasks', '/admin/background-tasks', 'collection', 'Background Tasks') }}
         {{ menu_item('imports', '/admin/imports', 'cube', 'Import Jobs') }}
         {{ menu_item('logs', '/admin/logs', 'document-text', 'Application Logs') }}
     {% endcall %}