feat(metrics): new-clients KPI and scheduled reminder dispatch

The dashboard promised a new-clients card the API never produced; the
metric now counts distinct customer emails whose earliest-ever booking
lands in the window, joining the other four KPIs with the same trend
comparison. The card grid rebalances for five items.

Reminder dispatch also had no trigger — the endpoint existed but
nothing called it. A scheduled GitHub Actions workflow now posts to it
every 15 minutes using the job-runner key, so reminders actually fire
once the two secrets are configured.

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project.md

@@ -96,6 +96,11 @@
   - reschedule hardened with the same validation as booking creation: appointment reschedules must fit an availability rule and avoid blocked days (`validateAppointmentTarget` is now a shared package-level helper); class bookings keep session-defined times
   - new repository methods `CancelPendingReminderJobsForBooking` / `DeletePendingReminderJobsForBooking` in pgx and in-memory implementations
   - remaining: live staging validation; SMS reminder channel exists in schema (`channel` column) but only `email` is dispatched — SMS reminders are a separate opt-in feature
+- `[done/partial]` Milestone 14: Metrics completion + reminder dispatch scheduling
+  - `DashboardMetrics` gained `NewClientsCount` — distinct customer emails whose earliest-ever booking (`starts_at`) lands in the window; a fifth KPI `new_clients` completes the set the demo data promised
+  - KPI grid rebalanced for five cards (`lg:grid-cols-3 xl:grid-cols-5`); `new_clients` maps to the existing `dashboard.kpi.newClients` i18n key
+  - reminder dispatch now has a real trigger: `.github/workflows/reminder-dispatch.yml` calls `POST /v1/internal/jobs/reminders/dispatch` every 15 minutes with `X-Bookra-Job-Key` from secrets (`BOOKRA_API_URL`, `BOOKRA_JOB_RUNNER_KEY`); jobs are timestamp-based so scheduler lateness delays but never skips
+  - remaining: live staging validation; the workflow no-ops gracefully until the two secrets are configured
 
 ## Overview
 Bookra is a Czech-first booking SaaS for small local service businesses. It targets salons, massage therapists, small clinics, repair shops, and small studios/clubs that need a simple public booking flow, internal schedule management, reminders, and basic business reporting without becoming a full ERP.