The merchant dashboard was showing subscription count as "Total Stores".
Add get_merchant_metrics() to MetricsProviderProtocol and implement it
in tenancy, billing, and customer providers. Dashboard now fetches real
stats from a new /merchants/core/dashboard/stats endpoint and displays
4 cards: active subscriptions, total stores, customers, team members.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Resolves the billing (core) → monitoring (optional) architecture violation
by moving CapacityForecastService to the monitoring module where it belongs.
- Create BillingMetricsProvider to expose subscription counts via stats_aggregator
- Move CapacitySnapshot model from billing to monitoring
- Replace direct MerchantSubscription queries with stats_aggregator calls
- Fix middleware test mocks to cover StoreDomain/MerchantDomain fallback chains
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
