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

@@ -0,0 +1,32 @@
+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