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/models.json

@@ -0,0 +1,12 @@
+{
+  "models": [
+    "meta-llama/llama-3.3-70b-instruct:free",
+    "google/gemma-3-27b-it:free",
+    "qwen/qwen3-235b-a22b:free"
+  ],
+  "notes": "2–3 OpenRouter model IDs. Prefer free-tier (:free) for owner repos; override via action input models= or edit this file. Paid models work the same (drop :free).",
+  "openrouter_base_url": "https://openrouter.ai/api/v1",
+  "temperature": 0,
+  "max_tokens": 4096,
+  "agreement_min": 2
+}