fix: phase 1 bugs — CSS tokens, pluralization, error handling, cross-platform tests

- Add missing --space-1 CSS token used by filter and detail components

- Fix active nav link losing styles on hover (CSS specificity)

- Correct Russian day pluralization (21 день, 22 дня, 25 дней)

- Show filter error banner even when stale race data is present

- Add cross-env for Windows-compatible npm test

- Add global JSON error handler in Express for malformed request bodies

- Replace stateless mock DB with in-memory store for correct DELETE/UPDATE behavior

Made-with: Cursor

frontend/src/lib/raceMetrics.ts

@@ -70,6 +70,22 @@ export function splitRacesByDate(races: Race[], now: Date = new Date()): { upcom
   };
 }
 
+function pluralizeDays(n: number): string {
+  const mod10 = n % 10;
+  const mod100 = n % 100;
+
+  if (mod100 >= 11 && mod100 <= 19) {
+    return "дней";
+  }
+  if (mod10 === 1) {
+    return "день";
+  }
+  if (mod10 >= 2 && mod10 <= 4) {
+    return "дня";
+  }
+  return "дней";
+}
+
 export function getRaceCountdownLabel(date: string, now: Date = new Date()): string {
   const today = new Date(now);
   today.setHours(0, 0, 0, 0);
@@ -80,13 +96,7 @@ export function getRaceCountdownLabel(date: string, now: Date = new Date()): str
   if (days <= 0) {
     return "сегодня";
   }
-  if (days === 1) {
-    return "через 1 день";
-  }
-  if (days < 5) {
-    return `через ${days} дня`;
-  }
-  return `через ${days} дней`;
+  return `через ${days} ${pluralizeDays(days)}`;
 }
 
 export function isCloseDistance(left: number, right: number): boolean {