test: minimal reusable workflow diagnostic

Adds ci-minimal.yml + ci-minimal-test.yml to diagnose the startup_failure
on the self-test reusable workflow call. To be removed after diagnosis.

Agent-Session: claude/reusable-ci-20260616

.github/workflows/ci-minimal.yml

@@ -0,0 +1,18 @@
+name: Minimal Reusable
+
+on:
+  workflow_call:
+    inputs:
+      test_input:
+        type: string
+        required: false
+        default: world
+
+permissions:
+  contents: read
+
+jobs:
+  hello:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "Hello ${{ inputs.test_input }}"