ci: bump wrangler-action to v4 (Node 24 runtime)

cloudflare/wrangler-action@v3 runs on Node.js 20, which GitHub force-
upgrades to Node 24 on 2026-06-16 and removes on 2026-09-16. v4 runs on
node24 and defaults to Wrangler v4 -- matching the npx wrangler (v4) used
by `npm run dev`/`deploy` locally, so CI and local deploy with the same
Wrangler major.

Author: rgilks

.github/workflows/ci.yml

@@ -124,7 +124,7 @@ jobs:
         run: npm run build
 
       - name: Deploy to Cloudflare Workers
-        uses: cloudflare/wrangler-action@v3
+        uses: cloudflare/wrangler-action@v4
         with:
           apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
           accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}