Self-hosted auto-updates from Gitea via PUC + proprietary licence

Vendors YahnisElsts/plugin-update-checker v5.7 under vendor/ and wires
it to poll updates.json on the repo main branch. WP surfaces new
versions via Dashboard → Updates on its normal twice-daily cadence.

PUC is vendored (not a submodule) so Gitea's archive/main.zip — the
download target — includes it.

Also relicenses from GPL-2.0-or-later to a proprietary licence granting
use only to authorised sites, with all other rights reserved. Plugin
URI + Author URI switched from the placeholder github.com URL to the
canonical Gitea repo.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vendor/plugin-update-checker/.gitattributes

@@ -0,0 +1,6 @@
+/.editorconfig export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/build/ export-ignore
+/examples/ export-ignore
+/phpcs.xml export-ignore