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/api/package.json

@@ -19,6 +19,7 @@
     "@hono/oidc-auth": "1.8.3",
     "@hono/zod-validator": "0.8.0",
     "drizzle-orm": "0.45.2",
+    "fractional-indexing": "^3.2.0",
     "hono": "4.12.23",
     "ical.js": "2.2.1",
     "mysql2": "3.22.4",