Add Linkding integration: new CT template (ct/linkding.sh) and installer (install/linkding-install.sh) to deploy Linkding as a container. Installer fetches the GitHub release, builds the frontend, compiles the SQLite ICU extension, creates .env with generated admin password, and installs systemd services (linkding, linkding-tasks). Also add frontend metadata (frontend/public/json/linkding.json) for the app catalog. Minor tweak: remove unused import_local_ip from install/wger-install.sh.
