fix(docker): chown /backup mount to nodejs on container startup

The docker-compose `./backup:/backup` mount was the only bind mount
not included in wait-for-db.sh's startup chown step. On a fresh
install (or any time the mount point is recreated), it stays
owned by root, and the nodejs (UID 1001) process running the
backup service gets EACCES when trying to mkdir under /backup.

Added /backup to both the chown list (root branch) and the
writable-check list (compose `user:` override branch), each guarded
by `[ -d /backup ]` so installs that don't use the bind mount —
native deployments, k8s with a different backup destination, etc. —
still boot cleanly.

Existing installs hit by this need a one-time host-side
  sudo chown -R 1001:1001 <host-mount-for-/backup>
because the on-disk ownership won't fix itself; the script only
chowns at startup, and the directory was already created with
the wrong ownership by Docker's mount-point auto-creation. From
this commit onward, fresh installs are correct from the first
boot.

backend/wait-for-db.sh

@@ -11,8 +11,15 @@ set -e
 # other than root skip this branch — they own permissions themselves and hit
 # the preflight check below instead.
 if [ "$(id -u)" = "0" ]; then
-  if ! chown -R nodejs:nodejs /app/storage /app/data /app/logs 2>/dev/null; then
-    echo "ERROR: failed to chown /app/storage, /app/data, /app/logs to nodejs (UID 1001)." >&2
+  # /backup is the docker-compose `./backup:/backup` mount used by the
+  # CRM + database backup writers. It's only chowned when it actually
+  # exists as a bind mount — installs that don't mount it (e.g. native
+  # / k8s deployments using a different backup destination) skip
+  # cleanly via the `[ -d /backup ]` guard.
+  _chown_dirs="/app/storage /app/data /app/logs"
+  [ -d /backup ] && _chown_dirs="$_chown_dirs /backup"
+  if ! chown -R nodejs:nodejs $_chown_dirs 2>/dev/null; then
+    echo "ERROR: failed to chown $_chown_dirs to nodejs (UID 1001)." >&2
     echo "  This usually means the host filesystem rejects chown (e.g. NFS without root squash" >&2
     echo "  disabled, or a SELinux/AppArmor policy blocking the operation)." >&2
     echo "  Workaround: pre-chown the host directories to 1001:1001 and pin 'user: \"1001:1001\"'" >&2
@@ -29,7 +36,15 @@ fi
 # followed by a confusing migration error and a restart loop.
 _uid="$(id -u)"
 _gid="$(id -g)"
-for _dir in /app/storage /app/data /app/logs; do
+# /backup is included here for symmetry with the root branch above:
+# when the compose `user:` override is set, the host operator is
+# expected to have chowned the bind mount themselves. Skip the
+# check when the mount isn't present so non-bind-mounted setups
+# (e.g. backup destination configured to local storage path) still
+# boot cleanly.
+_writable_dirs="/app/storage /app/data /app/logs"
+[ -d /backup ] && _writable_dirs="$_writable_dirs /backup"
+for _dir in $_writable_dirs; do
   if [ ! -w "$_dir" ]; then
     echo "ERROR: $_dir is not writable by UID $_uid." >&2
     echo "  Either drop the 'user:' override from your compose file so the container starts as" >&2