ci(deploy): pin upload/download-artifact to v3 for Gitea Actions

actions/upload-artifact@v4 and download-artifact@v4 use the
@actions/artifact v2+ client, which targets a github.com-only
backend and fails on Gitea / Forgejo / GHES with:

  GHESNotSupportedError: @actions/artifact v2.0.0+, upload-artifact@v4+
  and download-artifact@v4+ are not currently supported on GHES.

Pin both to v3, which uses the older artifact protocol that Gitea
Actions implements.

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

.gitea/workflows/deploy.yml

@@ -61,8 +61,11 @@ jobs:
             exit 1
           fi
 
+      # Pin to v3 — Gitea Actions implements the v3 artifact protocol.
+      # upload/download-artifact@v4 talk to a github.com-only backend and
+      # fail with GHESNotSupportedError on Gitea / Forgejo / GHES.
       - name: Upload dist artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: dist
           path: dist/
@@ -75,7 +78,7 @@ jobs:
 
     steps:
       - name: Download dist artifact
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v3
         with:
           name: dist
           path: dist/