feat(dashboard): revenue "year" tile toggles 365 days ↔ calendar YTD

Per request, keep the dashboard to four tiles rather than adding a fifth: the
"Revenue · last 365 days" tile is now clickable and toggles in place between
the trailing-365-day window and calendar year-to-date (since Jan 1).

- adminDashboard: new calendar-year cutoff + revenue.calendarYearMinor (same
  cash-basis paid_at window logic as the existing trio).
- StatCard gains an optional onClick (renders as a button); the year tile uses
  it, with a "Tap to switch window" hint for discoverability.
- bills.service CrmOverviewStats.revenue gains calendarYearMinor.

frontend/src/services/bills.service.ts

@@ -386,6 +386,9 @@ export interface CrmOverviewStats {
     monthMinor: number;
     quarterMinor: number;
     yearMinor: number;
+    /** Revenue since Jan 1 of the current year (calendar YTD). The
+     *  dashboard's "year" tile toggles between this and yearMinor. */
+    calendarYearMinor: number;
   };
   outstanding: {
     totalMinor: number;