fix: add @b9g/shovel as dependency in echo example

Without this, `bun run develop` resolves `shovel` from PATH (global
install) instead of node_modules/.bin, missing workspace features.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: brainkim

bun.lock

@@ -10,6 +10,7 @@
     "deploy": "wrangler deploy"
   },
   "dependencies": {
+    "@b9g/shovel": "^0.2.17",
     "@b9g/router": "workspace:*",
     "@b9g/platform": "workspace:*",
     "@b9g/platform-cloudflare": "workspace:*"