fix(install-log): pre-create /var/log/archipelago/ so non-root backend can write

The backend runs as `archipelago` and calls `install_log()` to append
audit lines to the install log on every install / update / remove /
start / stop / restart. Target path was /var/log/archipelago-container-installs.log,
which does not exist and cannot be created by the service because
/var/log/ is root-owned. OpenOptions errors were silently swallowed,
so the log was never written on any node.

Ship a tmpfiles.d rule that pre-creates /var/log/archipelago/ and
container-installs.log with archipelago:archipelago ownership. Move
the const path to match, keeping logs inside the directory logrotate
already rotates (image-recipe/configs/logrotate.conf). Install the
rule from both the ISO build and self-update, and apply it
immediately on self-update so existing nodes get a working log
without needing a reboot.

Verified on .228: file created, backend user can write, backend
binary rebuilt with new const.

scripts/self-update.sh

@@ -198,6 +198,17 @@ if [ -f "$REPO_DIR/image-recipe/configs/archipelago.service" ]; then
     fi
 fi
 
+# Install/refresh tmpfiles.d rules. The logs rule creates
+# /var/log/archipelago/ + container-installs.log with archipelago:archipelago
+# ownership so the non-root backend can append install audit lines.
+# Apply immediately so existing nodes don't need a reboot.
+if [ -f "$REPO_DIR/image-recipe/configs/archipelago-tmpfiles.conf" ]; then
+    sudo install -m 644 "$REPO_DIR/image-recipe/configs/archipelago-tmpfiles.conf" \
+        /usr/lib/tmpfiles.d/archipelago-logs.conf
+    sudo systemd-tmpfiles --create /usr/lib/tmpfiles.d/archipelago-logs.conf 2>/dev/null || true
+    ok "Log tmpfiles rule installed"
+fi
+
 # Restart service
 log "Restarting archipelago service..."
 sudo systemctl restart archipelago