ci: add Python 3.12 syntax check workflow

Creates CI badge on main branch for portfolio Level A standard.
Uses py_compile + import check (no test suite exists — stdlib only).

Satisfies CIAP-03

Author: GSD Planner

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - name: Syntax check
+        run: python -m py_compile agent/poll_once.py
+      - name: Import check
+        run: python -c "import agent.poll_once"