Add entrypoint fallback for missing bind-mounted scripts

- scripts/entrypoint.sh (new): prefers the live bind-mounted backup-cron.sh, but falls back to a copy baked into the image at build time if the mount is missing. If neither exists, it stays up and idle (instead of crash-looping) so the container remains reachable via console/exec for diagnosis.
- scripts/backup-cron.sh (updated): resolves db-backup.sh the same live-or-fallback way, re-checked on every loop iteration, so if the bind mount comes back healthy later, this container picks up the live scripts on its next backup run with no restart needed.
- scripts/backup.Dockerfile (updated): bakes all three scripts into the image under /app/scripts-default/ as the fallback, and sets the new wrapper as ENTRYPOINT.

scripts/backup-cron.sh

@@ -1,9 +1,27 @@
 #!/bin/sh
-# Entry point for the `backup` sidecar container. Runs db-backup.sh on a fixed
-# interval (default: daily). Kept deliberately simple — a sleep loop instead of a
-# cron daemon — so it works in a bare postgres:16-alpine image.
+# Entry point for the `backup` sidecar container's periodic loop. Runs
+# db-backup.sh on a fixed interval (default: daily) -- a sleep loop instead of
+# a cron daemon, kept deliberately simple so it works in a bare
+# postgres:16-alpine image.
+#
+# Resolves db-backup.sh the same way entrypoint.sh resolves this file: prefer
+# the live bind-mounted copy at /scripts (so edits don't need a rebuild), fall
+# back to the copy baked into the image at build time if the mount is
+# missing, empty, or stale. Resolving fresh on every loop iteration also means
+# that if the mount comes back healthy later (e.g. someone fixes the host
+# directory) this container picks it up on the very next run, with no
+# restart needed.
 set -eu
 
+resolve() {
+  # $1 = script filename, e.g. db-backup.sh
+  if [ -f "/scripts/$1" ]; then
+    echo "/scripts/$1"
+  else
+    echo "/app/scripts-default/$1"
+  fi
+}
+
 INTERVAL="${BACKUP_INTERVAL_SECONDS:-86400}"   # 86400 = once a day
 echo "[backup] sidecar started; interval=${INTERVAL}s, keep=${BACKUP_KEEP:-14}, dir=${BACKUP_DIR:-/backups}"
 
@@ -11,6 +29,7 @@ echo "[backup] sidecar started; interval=${INTERVAL}s, keep=${BACKUP_KEEP:-14},
 # immediate restore point instead of waiting a whole interval.
 sleep 20
 while true; do
-  sh /scripts/db-backup.sh || echo "[backup] run failed; will retry next interval" >&2
+  DB_BACKUP="$(resolve db-backup.sh)"
+  sh "$DB_BACKUP" || echo "[backup] run failed; will retry next interval" >&2
   sleep "$INTERVAL"
 done