Dogfood: run Gatekeep on this repo's PRs

Add .github/workflows/gatekeep-pr.yml with uses: ./ and
OPENROUTER_API_KEY from secrets. Forge-agnostic API helper for Gitea.

config/benchmarks.json

@@ -0,0 +1,15 @@
+{
+  "enabled": true,
+  "thresholds": {
+    "startup_ms_max": 15000,
+    "memory_mb_max": 1024,
+    "fps_min": 30
+  },
+  "notes": "Caller-configured verify-layer thresholds. Agent discovers how to run benches from README/package.json/Makefile; architecture-level perf debt is out of scope. Set a metric to null to skip it.",
+  "commands": {
+    "hint": "Optional explicit overrides. Empty = discover only.",
+    "benchmark": "",
+    "startup": "",
+    "memory": ""
+  }
+}