feat(automations): add schedule trigger source, selector and inputs

surfsense_backend/app/automations/triggers/builtin/schedule/inputs.py

@@ -0,0 +1,27 @@
+"""Build run inputs from a schedule fire."""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import Any
+
+
+def schedule_runtime_inputs(
+    *,
+    fired_at: datetime,
+    scheduled_for: datetime,
+    previous_last_fired_at: datetime | None,
+) -> dict[str, Any]:
+    """Calendar context for a scheduled run.
+
+    - ``fired_at`` — actual fire time
+    - ``scheduled_for`` — cron-derived target time for this fire
+    - ``last_fired_at`` — previous fire time, or null on first fire
+    """
+    return {
+        "fired_at": fired_at.isoformat(),
+        "scheduled_for": scheduled_for.isoformat(),
+        "last_fired_at": (
+            previous_last_fired_at.isoformat() if previous_last_fired_at else None
+        ),
+    }