feat: add sign-in flow, routing shell, and searchable book list

Pin @testing-library/jest-dom to ~6.9.1 (6.10.0 is npm-deprecated).

Claude-Session: https://claude.ai/code/session_01M9MLit5Ko3X4s7rzC5Kv7X

src/books/useGenres.ts

@@ -0,0 +1,11 @@
+import { useEffect, useState } from 'react'
+import { api, errorMessage, type Genre } from '../api'
+
+export function useGenres(): { genres: Genre[]; error: string | null } {
+  const [genres, setGenres] = useState<Genre[]>([])
+  const [error, setError] = useState<string | null>(null)
+  useEffect(() => {
+    api<Genre[]>('GET', '/genres').then(setGenres, (err) => setError(errorMessage(err)))
+  }, [])
+  return { genres, error }
+}