feat: Add final stacks (Batch 3)

Added stacks:
- plex (Media server)
- pterodactyl-panel (Game server management)
- gotosocial (ActivityPub/Fediverse)
- backrest (Backup UI)

All stacks include:
- compose.yml with proper configuration
- README.md with deployment info
- stack.toml for Komodo Resource Sync

TOTAL: 21 stacks ready for Komodo deployment!

stacks/backrest/README.md

@@ -0,0 +1,24 @@
+# Backrest
+
+💾 Backup Management UI
+
+## Deploy in Komodo
+
+**Pfad:** `stacks/backrest/`
+
+## Ports
+
+- `8080` - Web UI
+
+## Caddy
+
+```caddyfile
+backup.example.com {
+    reverse_proxy localhost:8080
+}
+```
+
+## Notes
+
+- UI für Restic Backups
+- Backup-Pfad anpassen

stacks/backrest/compose.yml

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+services:
+  backrest:
+    image: ghcr.io/gabm/backrest:latest
+    container_name: backrest
+    restart: unless-stopped
+    ports:
+      - "127.0.0.1:8080:8080"
+    volumes:
+      - backrest_config:/config
+      - /backups:/backups
+    networks:
+      - backrest-network
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:8080/api/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 10s
+
+volumes:
+  backrest_config:
+
+networks:
+  backrest-network:
+    driver: bridge

stacks/backrest/stack.toml

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+[[stacks]]
+name = "backrest"
+description = "Backup Management UI"
+compose_path = "compose.yml"