fix(service): Alarm creation without duration - aligns with ai_edge changes

Changes:
1. Modified create_from_mqtt to parse first_frame_time from MQTT data
2. Removed duration_minutes processing logic
3. Set duration_ms=None and last_frame_time=None on alarm creation
4. Updated _determine_alarm_level to handle duration_ms=None (returns level 2 for leave_post)

This ensures alarms are created with status=NEW and no duration/end time,
which will be populated later when the alarm is resolved.

Test: test_alarm_create_no_duration.py validates the new behavior.

Related: Task 2 of alarm status management fix

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

test_alarm_create_no_duration.py

@@ -0,0 +1,53 @@
+"""
+Test alarm creation without duration
+Verify:
+1. Alarm creation with duration_ms as None
+2. last_frame_time should be None
+3. first_frame_time should have value
+4. alarm_status should be NEW
+5. handle_status should be UNHANDLED
+"""
+import sys
+sys.path.insert(0, 'C:/Users/16337/PycharmProjects/service')
+
+from app.services.alarm_event_service import AlarmEventService
+
+def test_create_alarm_no_duration():
+    """Test creating alarm without duration"""
+    service = AlarmEventService()
+
+    mqtt_data = {
+        "alert_type": "leave_post",
+        "camera_id": "cam001",
+        "roi_id": "roi001",
+        "timestamp": "2026-02-12 14:30:00",
+        "first_frame_time": "2026-02-12 14:23:00",
+        "message": "Leave post alarm",
+        "confidence": 0.95,
+        # No longer sending duration_minutes
+    }
+
+    print("Creating alarm test...")
+    alarm = service.create_from_mqtt(mqtt_data)
+
+    # Verify
+    assert alarm is not None, "Alarm creation failed"
+    assert alarm.alarm_status == "NEW", f"Status should be NEW, but got {alarm.alarm_status}"
+    assert alarm.handle_status == "UNHANDLED", f"Handle status should be UNHANDLED, but got {alarm.handle_status}"
+    assert alarm.duration_ms is None, f"duration_ms should be None, but got {alarm.duration_ms}"
+    assert alarm.last_frame_time is None, f"last_frame_time should be None, but got {alarm.last_frame_time}"
+    assert alarm.first_frame_time is not None, "first_frame_time should have value"
+    assert alarm.alarm_level == 2, f"alarm_level should be 2 (general level), but got {alarm.alarm_level}"
+
+    print("[PASS] Test passed: Alarm created without duration")
+    print(f"   alarm_id: {alarm.alarm_id}")
+    print(f"   alarm_type: {alarm.alarm_type}")
+    print(f"   alarm_status: {alarm.alarm_status}")
+    print(f"   alarm_level: {alarm.alarm_level}")
+    print(f"   duration_ms: {alarm.duration_ms}")
+    print(f"   first_frame_time: {alarm.first_frame_time}")
+    print(f"   last_frame_time: {alarm.last_frame_time}")
+    print(f"   event_time: {alarm.event_time}")
+
+if __name__ == "__main__":
+    test_create_alarm_no_duration()