feat(04-01): install new deps + scaffold API test harness with Wave-0 RED stubs

- Add react-router@7, @dnd-kit/core, @dnd-kit/sortable, fractional-indexing to PWA
- Add fractional-indexing to API (rank generation server-side)
- ioredis NOT added (in-memory EventEmitter per RESEARCH Plan 02 justification)
- Create apps/api/test/setup.ts with afterEach DB cleanup for list tables
- Wire test.setupFiles in apps/api/vitest.config.ts
- Add 4 Wave-0 RED stub test files (LIST-01/02/03/04, D-04, D-11, D-07)
- All stubs run as todo, not import-error

apps/pwa/src/routes/ListDetail.test.tsx

@@ -0,0 +1,19 @@
+/**
+ * Wave-0 RED stubs for ListDetail component.
+ *
+ * Covers D-07: optimistic update — the editing member's change shows instantly,
+ * then reconciles against the server (rollback on rejection).
+ *
+ * Downstream plans implement the actual ListDetail.tsx component.
+ *
+ * Run: pnpm --filter @familysync/pwa test
+ */
+
+describe('ListDetail — D-07 optimistic update + rollback', () => {
+  it.todo('checking an item immediately updates the UI before server responds')
+  it.todo('unchecking an item immediately updates the UI before server responds')
+  it.todo('rolls back the checked state if the server PATCH returns an error')
+  it.todo('adding an item shows it in the list immediately (optimistic insert)')
+  it.todo('removes the optimistically-added item if the server POST returns an error')
+  it.todo('completed items sink to the "completed" section at the bottom (D-05)')
+})