feat(planner): add sortEasiestFirst utility for J4 swap context

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/planner/week.ts

@@ -75,6 +75,25 @@ export function isToday(dateStr: string): boolean {
 	return dateStr === todayStr;
 }
 
+const EFFORT_ORDER: Record<string, number> = { easy: 0, medium: 1, hard: 2 };
+
+/**
+ * Returns a new array of recipes sorted easiest first (effort ASC, cookTimeMin ASC).
+ * Used for the J4 mid-week swap context — different from variety-first sorting in J2.
+ */
+export function sortEasiestFirst<T extends { effort?: string | null; cookTimeMin?: number | null }>(
+	recipes: T[]
+): T[] {
+	return [...recipes].sort((a, b) => {
+		const ea = a.effort != null ? (EFFORT_ORDER[a.effort] ?? 99) : 99;
+		const eb = b.effort != null ? (EFFORT_ORDER[b.effort] ?? 99) : 99;
+		if (ea !== eb) return ea - eb;
+		const ta = a.cookTimeMin ?? Infinity;
+		const tb = b.cookTimeMin ?? Infinity;
+		return ta - tb;
+	});
+}
+
 /**
  * Formats a week range: "30. Mär – 5. Apr 2026".
  */