feat(observabilidade): tabela patterns + 6 detectores SQL
Adiciona tabela 'patterns' à BD sessions (UNIQUE por week_iso+pattern_key)
e helpers upsertPattern/getPatternsByWeek/getConsecutiveWeeks no SessionsDb.
Módulo patterns.ts implementa 6 detectores heurísticos para deteccão semanal:
1. skills_with_high_error_rate (ratio > 0.2, severity warning|action)
2. tools_low_efficiency (tool_calls/event_count médio > 0.5)
3. skill_tool_pairs (top 5 co-ocorrências)
4. duration_outliers (sessões > p95 com outcome != completed)
5. abandoned_sessions (event_count<3 AND outcome=unknown, >=5)
6. growing_complexity (avg tool_calls actual > anterior*1.3)
5 testes cobrem detector de erro, abandonadas, consecutive_weeks,
idempotência do upsert e toPatternRecord.
Refs Fase 6A · Desk #2059 · Project #65
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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