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.

defaults/providers.yaml

@@ -0,0 +1,17 @@
+# Bundled defaults — only providers you actually use.
+# `key` is a FREE-FORM secret / env var name (no required gatekeep_ prefix).
+# Put that name in the workflow step env, e.g. env: { OPENROUTER_API_KEY: ${{ secrets.OPENROUTER_API_KEY }} }
+
+agreement_min: 2
+temperature: 0
+max_tokens: 4096
+
+providers:
+  openrouter:
+    key: OPENROUTER_API_KEY
+    protocol: openai
+    models:
+      - google/gemma-4-31b-it:free
+      - google/gemma-4-26b-a4b-it:free
+      - cohere/north-mini-code:free
+      - nvidia/nemotron-3-nano-omni-30b-a3b-reasoning:free