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.
Remove duplicate source files from old ApiKeys/, Authentication/, and
Authorization/ folders that were already migrated to Common/Security/.
Update test namespace usings to match. Pin EFC Relational 10.0.5 to
resolve MSB3277 version conflict with Npgsql's transitive dependency.
Add LangVersion and TreatWarningsAsErrors to AppHost and ServiceDefaults.
