feat: create util stack consolidating utility services

Consolidates 6 utility services into a single util stack:
- drop (PairDrop) - P2P file sharing
- joplin (Joplin Server) - Note-taking and sync
- links (Linkwarden) - Bookmark manager with Meilisearch
- mattermost (Mattermost) - Team collaboration
- vault (Vaultwarden) - Password manager
- tandoor (Tandoor) - Recipe manager

Changes:
- Created util/compose.yaml with all 6 services
- Moved rtc_config.json to util directory
- Updated environment variables to use UTIL_ prefix
- Updated restic volume references to util_* names
- Container names changed from {service}_app to util_{service}
- Volume names changed from {service}_* to util_{service}_*
- Removed individual stack directories (drop, joplin, links, mattermost, vault, tandoor)
- Updated compose.yaml to include util/compose.yaml instead of individual stacks

All services maintain their original hostnames and functionality.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

restic/compose.yaml

@@ -19,18 +19,18 @@ services:
       - backup_core_redis_data:/volumes/core_redis_data:ro
       - backup_directus_uploads:/volumes/directus_uploads:ro
       - backup_directus_bundle:/volumes/directus_bundle:ro
-      - backup_mattermost_config:/volumes/mattermost_config:ro
-      - backup_mattermost_data:/volumes/mattermost_data:ro
-      - backup_mattermost_plugins:/volumes/mattermost_plugins:ro
-      - backup_tandoor_staticfiles:/volumes/tandoor_staticfiles:ro
-      - backup_tandoor_mediafiles:/volumes/tandoor_mediafiles:ro
+      - backup_util_mattermost_config:/volumes/mattermost_config:ro
+      - backup_util_mattermost_data:/volumes/mattermost_data:ro
+      - backup_util_mattermost_plugins:/volumes/mattermost_plugins:ro
+      - backup_util_tandoor_staticfiles:/volumes/tandoor_staticfiles:ro
+      - backup_util_tandoor_mediafiles:/volumes/tandoor_mediafiles:ro
       - backup_n8n_data:/volumes/n8n_data:ro
       - backup_filestash_data:/volumes/filestash_data:ro
-      - backup_linkwarden_data:/volumes/linkwarden_data:ro
-      - backup_linkwarden_meili_data:/volumes/linkwarden_meili_data:ro
+      - backup_util_linkwarden_data:/volumes/linkwarden_data:ro
+      - backup_util_linkwarden_meili_data:/volumes/linkwarden_meili_data:ro
       - backup_letsencrypt_data:/volumes/letsencrypt_data:ro
-      - backup_vaultwarden_data:/volumes/vaultwarden_data:ro
-      - backup_joplin_data:/volumes/joplin_data:ro
+      - backup_util_vaultwarden_data:/volumes/vaultwarden_data:ro
+      - backup_util_joplin_data:/volumes/joplin_data:ro
       - backup_jelly_config:/volumes/jelly_config:ro
       - backup_netdata_config:/volumes/netdata_config:ro
       - backup_ai_postgres_data:/volumes/ai_postgres_data:ro
@@ -91,20 +91,20 @@ volumes:
   backup_directus_bundle:
     name: core_directus_bundle
     external: true
-  backup_mattermost_config:
-    name: mattermost_config
+  backup_util_mattermost_config:
+    name: util_mattermost_config
     external: true
-  backup_mattermost_data:
-    name: mattermost_data
+  backup_util_mattermost_data:
+    name: util_mattermost_data
     external: true
-  backup_mattermost_plugins:
-    name: mattermost_plugins
+  backup_util_mattermost_plugins:
+    name: util_mattermost_plugins
     external: true
-  backup_tandoor_staticfiles:
-    name: tandoor_staticfiles
+  backup_util_tandoor_staticfiles:
+    name: util_tandoor_staticfiles
     external: true
-  backup_tandoor_mediafiles:
-    name: tandoor_mediafiles
+  backup_util_tandoor_mediafiles:
+    name: util_tandoor_mediafiles
     external: true
   backup_n8n_data:
     name: dev_n8n_data
@@ -112,20 +112,20 @@ volumes:
   backup_filestash_data:
     name: stash_filestash_data
     external: true
-  backup_linkwarden_data:
-    name: links_data
+  backup_util_linkwarden_data:
+    name: util_linkwarden_data
     external: true
-  backup_linkwarden_meili_data:
-    name: links_meili_data
+  backup_util_linkwarden_meili_data:
+    name: util_linkwarden_meili_data
     external: true
   backup_letsencrypt_data:
     name: proxy_letsencrypt_data
     external: true
-  backup_vaultwarden_data:
-    name: vault_data
+  backup_util_vaultwarden_data:
+    name: util_vaultwarden_data
     external: true
-  backup_joplin_data:
-    name: joplin_data
+  backup_util_joplin_data:
+    name: util_joplin_data
     external: true
 
   backup_jelly_config: