fix(auth): update PocketBase v0.23+ auth endpoint and rename users collection

- Replace deprecated /api/admins/auth-with-password with
  /api/collections/_superusers/auth-with-password in both the
  SvelteKit UI (pocketbase.ts) and Go scraper (pocketbase.go)
- Rename custom users collection to app_users to avoid name clash
  with PocketBase's built-in users auth collection
- Fix docker-compose volume mount path pb/pb_data -> pb_data so
  persisted data matches the entrypoint --dir flag
- Add PB_ADMIN_EMAIL/PB_ADMIN_PASSWORD env vars to pocketbase service
  so the superuser is auto-created on first boot

docker-compose.yml

@@ -45,10 +45,14 @@ services:
     image: ghcr.io/muchobien/pocketbase:latest
     #container_name: libnovel-pocketbase
     restart: unless-stopped
+    environment:
+      # Auto-create superuser on first boot (used by entrypoint.sh)
+      PB_ADMIN_EMAIL: "${POCKETBASE_ADMIN_EMAIL:-admin@libnovel.local}"
+      PB_ADMIN_PASSWORD: "${POCKETBASE_ADMIN_PASSWORD:-changeme123}"
     ports:
       - "${POCKETBASE_PORT:-8090}:8090"
     volumes:
-      - pb_data:/pb/pb_data
+      - pb_data:/pb_data
     healthcheck:
       test: ["CMD", "wget", "-qO-", "http://localhost:8090/api/health"]
       interval: 10s