fix(dayplan): sort the trip's dates with an explicit compare

ISO dates sort the same as plain strings, but a sort without a compare
function reads as an accident to anyone checking it, and SonarCloud flags
it as one. The three places that order the trip's dates now say how.

server/src/nest/days/day-removal.service.ts

@@ -209,7 +209,7 @@ export class DayRemovalService {
    */
   private renumber(tripId: number, rows: DayRow[], remaining: DayRow[]): string | null {
     // ISO dates sort as plain strings.
-    const sortedDates = rows.map(r => r.date).filter((d): d is string => !!d).sort();
+    const sortedDates = rows.map(r => r.date).filter((d): d is string => !!d).sort((a, b) => a.localeCompare(b));
     const setNumber = this.db.prepare('UPDATE days SET day_number = ? WHERE id = ?');
     const setNumberAndDate = this.db.prepare('UPDATE days SET day_number = ?, date = ? WHERE id = ?');