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/media/emby/docker-compose.yaml

@@ -1,19 +0,0 @@
-services:
-  emby:
-    image: emby/embyserver:latest
-    container_name: emby
-    environment:
-      - TZ=${TZ}
-    volumes:
-      - /path/to/emby:/config
-      - /path/to/media:/data
-      - /path/to/transcodes/emby:/transcode
-    ports:
-      - ${HTTP_PORT}:8096
-    restart: unless-stopped
-    networks:
-      - media-net
-
-networks:
-  media-net:
-    external: true

stacks/media/prowlarr/docker-compose.yaml

@@ -1,27 +0,0 @@
-services:
-  prowlarr:
-    container_name: prowlarr
-    image: lscr.io/linuxserver/prowlarr:latest
-    environment:
-      - PUID=${PUID}
-      - PGID=${PGID}
-      - TZ=${TZ}
-      - UMASK=${UMASK}
-    ports:
-      - ${HTTP_PORT}:9696
-    volumes:
-      - /path/to/prowlarr:/config
-      - /path/to/media:/data
-    restart: unless-stopped
-    healthcheck:
-      test: ["CMD-SHELL", "curl -f http://localhost:9696 || exit 1"]
-      interval: 15s
-      timeout: 5s
-      retries: 5
-      start_period: 20s
-    networks:
-      - media-net
-
-networks:
-  media-net:
-    external: true

stacks/media/qbittorrent/docker-compose.yaml

@@ -1,30 +0,0 @@
-services:
-  qbittorrent:
-    image: ghcr.io/hotio/qbittorrent:release-5.1.4
-    container_name: qbittorrent
-    privileged: true
-    environment:
-      - PUID=${PUID}
-      - PGID=${PGID}
-      - TZ=${TZ}
-      - UMASK=${UMASK}
-    volumes:
-      - /path/to/qbittorrent:/config
-      - /path/to/media/torrents:/data/torrents
-    ports:
-      - ${HTTP_PORT}:8080
-      - ${HTTP_PORT1}:8999
-      - ${HTTP_PORT1}:8999/udp
-    restart: always
-    healthcheck:
-      test: ["CMD-SHELL", "curl -f http://localhost:8080 || exit 1"]
-      interval: 15s
-      timeout: 5s
-      retries: 5
-      start_period: 30s
-    networks:
-      - media-net
-
-networks:
-  media-net:
-    external: true