feat: Flatten stack structure - all stacks directly in stacks/

- Removed all subdirectories
- Renamed compose.yml to <stack>-compose.yml
- Updated stack.toml to reference new compose file names
- Structure is now flat for easier Komodo sync

New structure:
stacks/
├── prometheus.toml
├── prometheus-compose.yml
├── grafana.toml
├── grafana-compose.yml
├── gotify.toml
├── gotify-compose.yml
├── vaultwarden.toml
├── vaultwarden-compose.yml
└── node-exporter.toml
└── node-exporter-compose.yml

stacks/node-exporter/compose.yml

@@ -1,28 +0,0 @@
-services:
-  node-exporter:
-    image: prom/node-exporter:latest
-    container_name: node-exporter
-    restart: unless-stopped
-    ports:
-      - "127.0.0.1:9100:9100"
-    volumes:
-      - /proc:/host/proc:ro
-      - /sys:/host/sys:ro
-      - /:/rootfs:ro
-    command:
-      - '--path.procfs=/host/proc'
-      - '--path.sysfs=/host/sys'
-      - '--path.rootfs=/rootfs'
-      - '--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)'
-    networks:
-      - monitoring
-    healthcheck:
-      test: ["CMD", "wget", "--spider", "-q", "http://localhost:9100/metrics"]
-      interval: 30s
-      timeout: 10s
-      retries: 3
-      start_period: 10s
-
-networks:
-  monitoring:
-    driver: bridge