fix: update mode chowns .go build cache to app user

- .go/ directory was root-owned from earlier builds
- Prevents 'permission denied' errors during go build

install.sh

@@ -106,7 +106,7 @@ if [ "${1:-}" = "-update" ]; then
         sudo_if chmod +x app
     fi
 
-    # Fix ownership of any new files.
+    # Fix ownership of all files (build cache may be root-owned from earlier builds).
     sudo_if chown -R "${APP_USER:-${SUDO_USER:-$(whoami)}}:${APP_USER:-${SUDO_USER:-$(whoami)}}" "$INSTALL_DIR" 2>/dev/null || true
 
     info "Restarting service..."