chore: mirror tmon GitHub protection setup

Add CODEOWNERS and a CI job named test so the Protect main ruleset
can require code-owner review and a green status check.

.github/CODEOWNERS

@@ -0,0 +1,3 @@
+# All changes need review from the maintainer before merge.
+# Only code-owner approvals count toward the required review on main.
+* @guillaumemeyer

.github/workflows/ci.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install test deps
+        run: python3 -m pip install --upgrade pip pytest
+
+      - name: Test
+        run: python3 -m pytest -q