fix(ci): downgrade artifact actions v4 -> v3 for Gitea compat

Gitea act_runner reports as GHES; @actions/artifact v2 (upload/
download-artifact@v4) uses the Twirp API Gitea does not implement,
failing with GHESNotSupportedError. v3 uses the artifact protocol
Gitea supports.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/actions/local-ci-build/action.yml

@@ -282,7 +282,7 @@ runs:
     # ── Upload build artifacts on success ─────────────────────────────────────
     - name: Upload artifacts
       if: success() && inputs.skip-artifact != 'true'
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v3
       with:
         name: ${{ steps.invoke-ci.outputs.artifact-name }}
         path: ${{ steps.invoke-ci.outputs.artifact-path }}\
@@ -292,7 +292,7 @@ runs:
     # ── Upload diagnostic logs on failure ─────────────────────────────────────
     - name: Upload diagnostic logs on failure
       if: failure()
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v3
       with:
         name: build-logs-${{ github.sha }}
         path: ${{ steps.invoke-ci.outputs.artifact-path }}\*.log