nextcloud: database engine mariadb 11.6 -> 12.3 (proven on 9202, R-462)

The ONE engine move in this series, and it is deliberate. Walked through the product's own
guarded Update on scratch guest 9202 during the update night: 217.4 s end to end, seed read back
through nextcloud's own front door before AND after, healthy after.

Permitted since R-469 (Slice 4 shipped): MARIADB_AUTO_UPGRADE=1 is already in this template and
converts the datadir. check-engine-major.py was run against this exact commit and ALLOWS it by
name, rather than being assumed to.

catalog_since -> 2026-09-22 (R-452).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

templates/nextcloud/.felhom.yml

@@ -10,7 +10,7 @@ subdomain: "cloud"
 slug: "nextcloud"
 # catalog_since: the date THIS repo last changed this app's pinned images. Any commit that
 # changes an image: line must set this to the same day (see CLAUDE.md).
-catalog_since: "2026-07-18"
+catalog_since: "2026-09-22"
 
 # --- Resource hints (displayed on deploy screen) ---
 resources:

templates/nextcloud/docker-compose.yml

@@ -70,7 +70,7 @@ services:
       - "traefik.http.routers.nextcloud.middlewares=nextcloud-redirect"
 
   nextcloud-db:
-    image: mariadb:11.6
+    image: mariadb:12.3
     container_name: nextcloud-db
     restart: unless-stopped
     environment: