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/prometheus/compose.yml

@@ -1,32 +0,0 @@
-services:
-  prometheus:
-    image: prom/prometheus:latest
-    container_name: prometheus
-    restart: unless-stopped
-    ports:
-      - "127.0.0.1:9090:9090"
-    volumes:
-      - prometheus_data:/prometheus
-      - prometheus_config:/etc/prometheus
-    command:
-      - '--config.file=/etc/prometheus/prometheus.yml'
-      - '--storage.tsdb.path=/prometheus'
-      - '--storage.tsdb.retention.time=15d'
-      - '--web.console.libraries=/etc/prometheus/console_libraries'
-      - '--web.console.templates=/etc/prometheus/consoles'
-    networks:
-      - monitoring
-    healthcheck:
-      test: ["CMD", "wget", "--spider", "-q", "http://localhost:9090/-/healthy"]
-      interval: 30s
-      timeout: 10s
-      retries: 3
-      start_period: 10s
-
-volumes:
-  prometheus_data:
-  prometheus_config:
-
-networks:
-  monitoring:
-    driver: bridge