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/grafana.toml

@@ -0,0 +1,25 @@
+[stack]
+name = "Grafana"
+description = "Grafana Dashboards & Visualisierung"
+version = "1.0.0"
+category = "monitoring"
+author = "nocci"
+
+[compose]
+file = "grafana-compose.yml"
+
+[variables.secrets]
+grafana-admin-user = "Admin Username"
+grafana-admin-pass = "Admin Password"
+
+[ports]
+grafana = "3000"
+
+[volumes]
+grafana_data = "/var/lib/grafana"
+
+[healthcheck]
+endpoint = "http://localhost:3000/api/health"
+interval = "30s"
+timeout = "10s"
+retries = 3