Move SealShare from GitHub to Gitea only

The workflows live in .gitea/workflows. The Docker workflow logs in to
the Gitea container registry with REGISTRY_TOKEN (Gitea's job token cannot
publish packages yet), publishes gitea.nonameweb.ch/nonameweb/sealshare
with a registry build cache, and makes the release on Gitea with the
version's section of the changelog as its notes.

The README, the website's quick start, both compose files and the image
label point to Gitea; the changelog announces the new image name and
links Gitea. GiteaOnlyTest keeps GitHub and ghcr.io out.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

docker-compose.example.yml

@@ -18,7 +18,7 @@ services:
   # SealShare Application (FrankenPHP/Octane)
   # ------------------------------------------
   app:
-    image: ghcr.io/surtic86/sealshare:latest
+    image: gitea.nonameweb.ch/nonameweb/sealshare:latest
     restart: unless-stopped
     ports:
       - "80:80"       # HTTP
@@ -71,7 +71,7 @@ services:
   # Scheduler - Runs cleanup for expired shares
   # ------------------------------------------
   scheduler:
-    image: ghcr.io/surtic86/sealshare:latest
+    image: gitea.nonameweb.ch/nonameweb/sealshare:latest
     restart: unless-stopped
     entrypoint: ["php", "artisan", "schedule:work"]
     volumes: