Add support for deploying Discourse as a container: adds ct/discourse.sh (container build/install/update flow and resource defaults), frontend/public/json/discourse.json (app metadata, install resources, and notes), and install/discourse-install.sh (full installer that installs dependencies, Postgres/Node/Ruby, clones the Discourse repo, generates secrets and DB password saved to /opt/discourse/.env, installs gems and yarn, precompiles assets, runs migrations, creates an admin user, sets up a systemd service and nginx reverse proxy, and enables required services). Admin user 'admin' is created with a generated password stored in the .env file.
