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>

tests/test_cron_reminder.py

@@ -0,0 +1,57 @@
+"""Tests for the reminder cron executor."""
+
+from unittest.mock import AsyncMock
+
+import pytest
+
+from cron.reminder import execute_reminder
+
+
+class TestReminderExecutor:
+    @pytest.mark.asyncio
+    async def test_sends_reminder_to_room(self):
+        job = {
+            "id": "j1",
+            "name": "Daily Check",
+            "config": {"message": "Check your portfolio"},
+            "targetRoom": "!room:finance",
+        }
+        send_text = AsyncMock()
+        result = await execute_reminder(job=job, send_text=send_text)
+
+        assert result["status"] == "success"
+        send_text.assert_called_once()
+        room_id, msg = send_text.call_args[0]
+        assert room_id == "!room:finance"
+        assert "Check your portfolio" in msg
+        assert "Daily Check" in msg
+        assert "\u23f0" in msg  # alarm clock emoji
+
+    @pytest.mark.asyncio
+    async def test_returns_error_without_message(self):
+        job = {
+            "id": "j1",
+            "name": "Empty",
+            "config": {},
+            "targetRoom": "!room:test",
+        }
+        send_text = AsyncMock()
+        result = await execute_reminder(job=job, send_text=send_text)
+
+        assert result["status"] == "error"
+        assert "message" in result["error"].lower()
+        send_text.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_empty_message_returns_error(self):
+        job = {
+            "id": "j1",
+            "name": "Empty",
+            "config": {"message": ""},
+            "targetRoom": "!room:test",
+        }
+        send_text = AsyncMock()
+        result = await execute_reminder(job=job, send_text=send_text)
+
+        assert result["status"] == "error"
+        send_text.assert_not_called()