Add reusable ci.yml standard workflow (#19)

Reusable workflow_call CI keystone (ADR 2026-06-16). QA-approved 6adf255d.

.github/workflows/ci-self-test.yml

@@ -0,0 +1,27 @@
+# Self-test: exercises the reusable ci.yml on this repo itself.
+# Uses tests: none (peptide-e2e is a Playwright/Node repo, no PHP suite).
+# permissions: contents: write is required at the caller level — any caller of
+# ci.yml must declare this so the phpcs job can commit phpcbf fixes back to the
+# PR branch. Even with phpcs_autofix: false here, the permission must be declared
+# for the reusable workflow to pass GH's startup permission-escalation check.
+
+name: CI Self-Test (reusable ci.yml)
+
+on:
+  push:
+    branches: [main, 'claude/**']
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: write  # required: called ci.yml phpcs job declares job-level write for phpcbf
+
+jobs:
+  ci:
+    uses: ./.github/workflows/ci.yml
+    with:
+      tests: none
+      enforce_300: false
+      has_js: false
+      phpcs_autofix: false
+    secrets: inherit