Add default board to new projects, remove uncategorized pseudo-board (#29874)

On creation of an empty project (no template) a default board will be
created instead of falling back to the uneditable pseudo-board.

Every project now has to have exactly one default boards. As a
consequence, you cannot unset a board as default, instead you have to
set another board as default. Existing projects will be modified using a
cron job, additionally this check will run every midnight by default.

Deleting the default board is not allowed, you have to set another board
as default to do it.

Fixes #29873
Fixes #14679 along the way
Fixes #29853

Co-authored-by: delvh <dev.lh@web.de>
(cherry picked from commit e5160185ed65fd1c2bcb2fc7dc7e0b5514ddb299)

Conflicts:
	options/locale/locale_en-US.ini
	trivial conflict because Forgejo strings do not have
	surrounding double quotes

web_src/js/features/repo-projects.js

@@ -58,7 +58,6 @@ async function initRepoProjectSortable() {
   createSortable(mainBoard, {
     group: 'project-column',
     draggable: '.project-column',
-    filter: '[data-id="0"]',
     animation: 150,
     ghostClass: 'card-ghost',
     delayOnTouchOnly: true,