Add pattern recognition for repeated workflows

[Jmeg8r]

Implement detection of recurring workflow patterns across sessions. When Cortex notices the developer repeatedly performs similar sequences, it should surface this as a potential automation opportunity or include it in briefings.

Acceptance Criteria

• Workflow pattern extraction from session events
• Pattern frequency tracking and scoring
• Integration with briefing generation (surface common patterns)
• Configurable threshold for pattern significance
• Tests for pattern detection accuracy