chore: backend infrastructure improvements

- add URI versioning: global prefix changed to api/v1, all frontend call sites updated
- add AbortSignal.timeout to all outbound fetch calls (10s API, 15s scrapers)
- add X-Request-Id response header and requestId field in error payloads
- add response compression via @fastify/compress (gzip + brotli)
- add security headers via @fastify/helmet with CSP for the Vite SPA
- tune pg pool: max 20, idle/connection/statement timeouts on app and migration pools
- add GET /api/v1/health endpoint via @nestjs/terminus with DB connectivity check

client/src/features/book/components/BookListRow.vue

@@ -69,7 +69,7 @@ async function setRating(star: number) {
   const newRating = localRating.value === star ? null : star
   localRating.value = newRating
   emit('rating-change', newRating)
-  await api(`/api/books/${props.book.id}/metadata`, {
+  await api(`/api/v1/books/${props.book.id}/metadata`, {
     method: 'PATCH',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify({ rating: newRating }),