fix(ci): migrate Docker registry from GHCR to Gitea

- Change REGISTRY from ghcr.io to git.farh.net
- Replace GHCR login with Gitea Container Registry login using REGISTRY_TOKEN
- Move workflow from .github/workflows to .gitea/workflows

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitea/workflows/ci.yml

@@ -72,9 +72,9 @@ jobs:
       - name: Log in to Gitea Container Registry
         uses: docker/login-action@v3
         with:
-          registry: git.farh.net
+          registry: ${{ env.REGISTRY }}
-          username: cartsnitch
+          username: ${{ github.actor }}
-          password: ${{ secrets.GITEA_TOKEN }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Extract metadata
         id: meta