feat(realunit): add cron-cached admin KPI stats endpoint

[TaprootFreak]

What

Adds a new cron-cached aggregate admin endpoint GET /v1/realunit/admin/stats (role REALUNIT/ADMIN) returning RealUnit KPIs. Mirrors the existing StatisticService cron/cache pattern: an hourly @DfxCron refreshes an in-memory cache; the route just returns it. Process.UPDATE_REALUNIT_STATS is added so the job can be disabled like other cron processes.

A companion frontend PR lives in DFXswiss/services; the DTO field names below are the shared contract.

Response shape

RealUnitStatsDto {
  updated: Date;
  growth:       { accounts: Period; wallets: Period };
  kycFunnel:    { step: KycStepName; reached: Period; completed: Period }[];
  registration: { started: Period; inReview: Period; completed: Period };
  trading:      { buyVolumeChf: Period; buyCount: Period; sellVolumeChf: Period; sellCount: Period };
}
Period { total: number; last30Days: number; last7Days: number }

Each KPI is reported over three windows: all-time total, last30Days, last7Days. New reusable aggregate query helpers were added (all SQL-side, grouped counts/sums): KycAdminService.getKycStepCounts, UserDataService.getNewUserDataCount, UserService.getNewUserCount, TransactionService.getAssetTradingStats.

Scoping / data-source notes

• growth: global new UserData (accounts) / User (wallets) by created. The API has no RealUnit-app client tag, so this is platform-wide growth, not RealUnit-only.
• kycFunnel: counts over KycSteps whose name is in contextRequiredSteps(REALUNIT_BUY) (canonical helper, not hardcoded). KycStep has no context column, so this is the step set used for RealUnit buy, not a per-user RealUnit filter; drop-off is derivable across steps. completed = steps with ReviewStatus.COMPLETED.
• registration: the RealUnit-specific REALUNIT_REGISTRATION KycStep — started (all), inReview (in-progress/review statuses), completed.
• trading: completed transactions on the REALU asset — CHF volume (SUM(amountInChf), rounded to Config.defaultVolumeDecimal) and counts, split by buy/sell.
• Only flat aggregate counts/sums, no per-user attributes, so not re-identifying. A suppression threshold can be added later if Legal requests.

Tests

100% coverage on new code (new service, new DTO, new helper methods). Cron is not auto-fired in tests; doUpdate() is called directly then getStats() asserted. format / lint / type-check / full jest suite all green locally.