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/dev-tools/ollama/docker-compose.yaml

@@ -1,44 +0,0 @@
-services:
-  ollama:
-    # Uncomment below for GPU support
-    # deploy:
-    #   resources:
-    #     reservations:
-    #       devices:
-    #         - driver: nvidia
-    #           count: 1
-    #           capabilities:
-    #             - gpu
-    volumes:
-      - /path/to/ollama:/root/.ollama
-    # Uncomment below to expose Ollama API outside the container stack
-    ports:
-      - "${HTTP_PORT2}:11434"
-    container_name: ollama
-    pull_policy: always
-    tty: true
-    restart: unless-stopped
-    image: ollama/ollama:latest
-    networks:
-      - openai-net
-
-  open-webui:
-    image: ghcr.io/open-webui/open-webui:latest
-    container_name: open-webui
-    volumes:
-      - /path/to/open-webui:/app/backend/data
-    depends_on:
-      - ollama
-    ports:
-      - "${HTTP_PORT}:8080"
-    environment:
-      - "OLLAMA_BASE_URL=http://ollama:11434"
-    extra_hosts:
-      - host.docker.internal:host-gateway
-    restart: unless-stopped
-    networks:
-      - openai-net
-
-networks:
-  openai-net:
-    external: true