Aggregate Security Metrics by Month

Problem

Given a list of security operation events, aggregate them into monthly reporting metrics. Each event is a dictionary with keys date (YYYY-MM-DD), severity ("low", "medium", "high", "critical"), and resolved (true or false). Return a list of monthly summaries sorted by month, where each summary contains the month (YYYY-MM), total event count, unresolved event count, and counts for each severity.

Constraints

• 1 <= len(events) <= 10^5
• Each event contains keys date, severity, and resolved
• date is always a valid string in YYYY-MM-DD format
• severity is one of low, medium, high, critical