stacks: remove 9 folders, update stack count in README

Removed: ollama (AI-related concerns), emby/qbittorrent/prowlarr
(media-download concerns), bookstack (being deprecated in the
homelab), and mariadb-latest/mysql-8/postgres-18-alpine/valkey-9.0-
alpine (build-only base-image factories - nothing connects to them,
they add no portfolio value on their own; real per-app DB usage,
e.g. Kodi's own mariadb service, already lives in that app's stack
folder and is unaffected).

Stack count updated 53 -> 44 in both README references.

stacks/productivity/bookstack/docker-compose.yaml

@@ -1,63 +0,0 @@
----
-services:
-  bookstack:
-    image: lscr.io/linuxserver/bookstack:latest
-    container_name: bookstack
-    environment:
-      - PUID=${PUID}
-      - PGID=${PGID}
-      - TZ=${TZ}
-      - APP_URL=https://subdomain.example.com
-      - DB_HOST=bookstack_db
-      - DB_PORT=${DB_PORT}
-      - DB_USER=${DB_USER}
-      - DB_PASS=${DB_PASS}
-      - DB_DATABASE=${DB_DATABASE}
-      - APP_DEFAULT_DARK_MODE=true
-    volumes:
-      - /path/to/bookstack/bookstack_app_data:/config
-    ports:
-      - ${HTTP_PORT}:80
-    restart: unless-stopped
-    depends_on:
-      bookstack_db:
-        condition: service_healthy
-    healthcheck:
-      test: ["CMD-SHELL", "wget -qO- http://127.0.0.1:80/ || exit 1"]
-      interval: 15s
-      timeout: 5s
-      retries: 5
-      start_period: 30s
-    networks:
-      - bookstack-net
-
-  bookstack_db:
-    image: lscr.io/linuxserver/mariadb:latest
-    container_name: bookstack_db
-    environment:
-      - PUID=${PUID}
-      - PGID=${PGID}
-      - TZ=${TZ}
-      - MYSQL_ROOT_PASSWORD=${DB_ROOT_PASSWORD}
-      - MYSQL_DATABASE=${DB_DATABASE}
-      - MYSQL_USER=${DB_USER}
-      - MYSQL_PASSWORD=${DB_PASSWORD}
-    volumes:
-      - /path/to/bookstack/bookstack_db_data:/config
-    restart: unless-stopped
-    healthcheck:
-      test:
-        [
-          "CMD-SHELL",
-          "mysqladmin ping -h localhost -u${DB_USER} -p${DB_PASSWORD} || exit 1",
-        ]
-      interval: 10s
-      timeout: 5s
-      retries: 10
-      start_period: 20s
-    networks:
-      - bookstack-net
-
-networks:
-  bookstack-net:
-    external: true