Document the gamesportal integration and fill in older gaps Adds Games Portal to the Integrations list, a new section on per-user notifications and the external notification API, and expands the previously-empty account-page settings section. Also fixes two pre-existing omissions found while doing this pass: qBittorrent was missing from the Integrations bullet and Project Structure's module list, and the account page's notification preferences were never documented at all despite shipping a while ago.
Add full documentation pages migrated from README Moves the detailed installation, configuration, admin-panel-guide, updating/rollback, security, project-structure and testing content out of the main README into dedicated wiki pages, with a Home landing page and a sidebar linking all of them. Nothing was dropped, only relocated (with a couple of small clauses reunited with their proper home page).