fix: prevent watchtower from checking images on container restart

Added --no-startup flag to Watchtower command in compose.yml.
Previously, Watchtower would check for image updates on every container
startup/restart. Now only runs at scheduled time (midnight daily).

.claude/JOURNAL.md

@@ -51,3 +51,6 @@ This journal tracks substantive work on documents, diagrams, and documentation c
 
 16. **Task - Cleanup startup scripts**: Removed obsolete nvidia-smi script and renumbered ensure_groups<br>
     **Result**: Deleted 01_nvidia-smi.sh (GPU detection now uses separate nvidia/cuda container spawned by jupyterhub_config.py), renamed 02_ensure_groups.py to 01_ensure_groups.py for sequential ordering, bumped version to 3.3.2
+
+17. **Task - Fix Watchtower refresh frequency**: Investigated and fixed Watchtower running image checks on every container restart instead of daily<br>
+    **Result**: Added `--no-startup` flag to Watchtower command in compose.yml, preventing image refresh checks on container startup/restart - now only runs at scheduled midnight (cron `0 0 * * *`)

compose.yml

@@ -98,7 +98,7 @@ services:
     image: nickfedor/watchtower:latest
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock:rw # to control docker and refresh images
-    command: --cleanup --schedule "0 0 * * *" # run every day at midnight
+    command: --cleanup --no-startup --schedule "0 0 * * *" # daily at midnight only, no check on startup
     security_opt:
       - seccomp:unconfined #optional
     depends_on: