feat(MAT-174): Add cron job scheduler and executors

Cron package that syncs jobs from matrixhost portal API, schedules execution
with timezone-aware timing, and posts results to Matrix rooms. Includes
Brave Search, reminder, and browser scrape (placeholder) executors with
formatter. 31 pytest tests.

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

cron/reminder.py

@@ -0,0 +1,20 @@
+"""Simple reminder executor for cron jobs."""
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+async def execute_reminder(job: dict, send_text, **_kwargs) -> dict:
+    """Post a reminder message to a Matrix room."""
+    config = job.get("config", {})
+    message = config.get("message", "")
+    target_room = job["targetRoom"]
+
+    if not message:
+        return {"status": "error", "error": "No reminder message configured"}
+
+    text = f"\u23f0 **{job['name']}:** {message}"
+    await send_text(target_room, text)
+
+    return {"status": "success"}