Group parent/child routes in admin route table

Visually indent child routes under their parent with tree connectors,
and make dragging a parent move all its children as a unit.

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

.beans/nuzlocke-tracker-hit0--group-parentchild-routes-in-admin-route-table.md

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+---
+# nuzlocke-tracker-hit0
+title: Group parent/child routes in admin route table
+status: completed
+type: feature
+priority: normal
+created_at: 2026-02-13T13:33:36Z
+updated_at: 2026-02-13T13:34:42Z
+---
+
+Visually indent child routes under their parent in the admin route table. Dragging a parent route moves all its children with it. Children cannot be independently dragged to a new position.
+
+## Checklist
+- [x] Add organizeRoutes() function to AdminGameDetail.tsx
+- [x] Replace SortableRouteRow with SortableRouteGroup using multiple tbody elements
+- [x] Update SortableContext to only track group IDs
+- [x] Update handleDragEnd for group-aware reordering
+- [x] Handle edge cases (standalone routes, orphan children)
+- [x] Verify frontend build passes