Query event:goal dimension with visitors, events, and conversion_rate
metrics via the existing POST /api/v2/query endpoint. Shows goal name,
unique conversions, and conversion rate percentage in a dedicated card.
- Add GoalConversion model with name, visitors, events, conversionRate
- Add 9th concurrent query in StatsRepository (try/catch for graceful
degradation when no goals are configured)
- Add GoalConversionsSection composable; hidden when no goals exist
- Add goalConversions to DashboardData with default emptyList() for
backward cache compatibility
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>