Localization sweep: shared es-CR dates module, no more en-US strays

src/lib/dates.ts is the single source for month names and date
formatting; the three per-page month arrays are gone (with an
off-by-one guard — the shared array is 1-indexed). formatDate and the
Analytics chart tooltips now speak es-CR, Analytics headings are
Spanish, and the cycle selector says 'Todo el período' (UX-19, FE-17,
UX-07).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/format.ts

@@ -1,3 +1,5 @@
+import { formatShortDate } from './dates';
+
 export function formatAmount(amount: number, currency: string) {
   const abs = Math.abs(amount);
   if (currency === 'BTC') return abs.toFixed(8);
@@ -17,5 +19,5 @@ export function formatLocalDatetime(d: Date): string {
 }
 
 export function formatDate(dateStr: string) {
-  return new Date(dateStr).toLocaleDateString('en-US', { month: 'short', day: 'numeric' });
+  return formatShortDate(dateStr);
 }