Instruments FeatureEvaluationService with System.Diagnostics.Metrics (Counter + IMeterFactory). Accumulates per-feature/day evaluation counts in-process, flushed every 30s to a new FeatureUsageDaily Postgres table via PostgreSQL ON CONFLICT upsert. Caches dashboard query results for 180s in IMemoryCache. New GET /api/v1/environments/{id}/usage endpoint returns top-10 features last day and 14-day per-day breakdown. Admin dashboard shows two ApexCharts bar charts: top features and evaluations by day with per-flag hover tooltip.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
