ci: include bun test in the gate

Phase 5 of the toolchain rollout: finalize the gate.
- gate is now the full chain: typecheck -> format -> lint -> knip -> test
- ci.yml already runs 'bun run gate' (added in phase 2), so CI now
  enforces the complete chain on every push/PR
- no coverage threshold: relaxed for a website (tests run, but we don't
  gate on a percentage the way the library repo does)

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

Author: cevheri

package.json

@@ -13,7 +13,7 @@
     "lint": "oxlint",
     "knip": "knip",
     "test": "bun test",
-    "gate": "bun run typecheck && bun run format && bun run lint && bun run knip"
+    "gate": "bun run typecheck && bun run format && bun run lint && bun run knip && bun run test"
   },
   "dependencies": {
     "@astrojs/sitemap": "^3.7.3",