feat(frontend): race form, start time selects, calendar views, day page

- Hide org schedule fields when editing a past race; isRaceDateInPast helper
- StartTimeSelects (HH:mm:ss) and optional ?date= prefill on new race
- Full-card link to edit for races needing result entry; shadow token
- List/calendar toggle (sessionStorage); year grid and month focus views
- Date hover popover and /races/day/:ymd page with Add button
- Docs plan-korrektirovok-starty.md and startTime API note; client 0.4.0

Made-with: Cursor

frontend/src/lib/raceMetrics.ts

@@ -12,6 +12,13 @@ export function parseRaceDate(date: string): Date {
   return parsed;
 }
 
+/** Дата старта (календарный день) строго раньше сегодняшней полуночи по локали. */
+export function isRaceDateInPast(raceDate: string, now: Date = new Date()): boolean {
+  const today = new Date(now);
+  today.setHours(0, 0, 0, 0);
+  return parseRaceDate(raceDate).getTime() < today.getTime();
+}
+
 export function parseFinishTimeToSeconds(value: string | null): number | null {
   if (!value) {
     return null;