feat(dev_tools): add diagnostics hub with permissions audit tool

Evolve the platform-debug page into a diagnostics hub with sidebar
explorer layout. Add permissions audit API that introspects all
registered page routes and reports auth/permission enforcement status.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/dev_tools/definition.py

@@ -82,7 +82,7 @@ dev_tools_module = ModuleDefinition(
                     ),
                     MenuItemDefinition(
                         id="platform-debug",
-                        label_key="dev_tools.menu.platform_debug",
+                        label_key="dev_tools.menu.diagnostics",
                         icon="search",
                         route="/admin/platform-debug",
                         order=40,