ci(root): add oh-my-agent auto-update workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gracefullight

.github/workflows/update-oma.yml

@@ -0,0 +1,18 @@
+name: Update oh-my-agent
+
+on:
+  schedule:
+    - cron: "0 9 * * 1" # Every Monday at 09:00 UTC
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: first-fluke/oh-my-agent/action@v1