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/vaultwarden/stack.toml

@@ -1,24 +0,0 @@
-[stack]
-name = "Vaultwarden"
-description = "Password Manager (Bitwarden-kompatibel)"
-version = "1.0.0"
-category = "security"
-author = "nocci"
-
-[compose]
-file = "compose.yml"
-
-[variables.secrets]
-vaultwarden-admin-token = "Admin API Token (openssl rand -base64 48)"
-
-[ports]
-vaultwarden = "80"
-
-[volumes]
-vaultwarden_data = "/data"
-
-[healthcheck]
-endpoint = "http://localhost:80/alive"
-interval = "30s"
-timeout = "10s"
-retries = 3