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/plex/README.md

@@ -0,0 +1,24 @@
+# Plex
+
+🎬 Media Server (Commercial)
+
+## Deploy in Komodo
+
+**Pfad:** `stacks/plex/`
+
+## Ports
+
+- `32400` - Web UI & API
+
+## Caddy
+
+```caddyfile
+plex.example.com {
+    reverse_proxy localhost:32400
+}
+```
+
+## Notes
+
+- PLEX_CLAIM Token von plex.tv nötig
+- Hardware Transcoding: `/dev/dri` mounten