fix(demo): resolve tag from input first (workflow_dispatch ref_name is the branch)

GITHUB_REF_NAME is 'main' on workflow_dispatch, so the old ${REF:-input} order
labeled every dispatched deploy 'main'. Prefer github.event.inputs.tag.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/deploy-demo.yml

@@ -64,7 +64,9 @@ jobs:
 
       - name: Resolve tag
         id: tag
-        run: echo "tag=${GITHUB_REF_NAME:-${{ github.event.inputs.tag }}}" >> "$GITHUB_OUTPUT"
+        # On workflow_dispatch GITHUB_REF_NAME is the branch (e.g. main), so prefer
+        # the explicit input; on a tag push the input is empty and ref_name is the tag.
+        run: echo "tag=${{ github.event.inputs.tag || github.ref_name }}" >> "$GITHUB_OUTPUT"
 
       # 1) Reuse prebuilt WASM: snapshot the current registry into manifest-<tag>
       #    (no build, no upload). Fails if the WASM was never published — run