test(variety): extract and test sub-score/warnings pure functions

- Extract computeSubScores() and computeWarnings() to variety.ts
- 18 unit tests covering formulas, boundaries, clamping, edge cases:
  - proteinDiversity: repeats × 2 penalty, clamped to 0
  - ingredientOverlap: overlaps × 1.5 penalty, clamped to 0
  - effortBalance: easy-hard diff × 1.5, total=0 → 10
  - warnings: repeat≥2 days, overlap≥2 days, duplicates

Addresses QA blockers: untested business logic in sub-score derivations.

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

frontend/src/lib/planner/variety.ts

@@ -0,0 +1,88 @@
+interface TagRepeat {
+	tagType?: string;
+	tagName?: string;
+	days?: string[];
+}
+
+interface IngredientOverlap {
+	ingredientName?: string;
+	days?: string[];
+}
+
+interface SubScoreInput {
+	tagRepeats: TagRepeat[];
+	ingredientOverlaps: IngredientOverlap[];
+	easy: number;
+	medium: number;
+	hard: number;
+}
+
+export interface SubScores {
+	proteinDiversity: number;
+	ingredientOverlap: number;
+	effortBalance: number;
+}
+
+export function computeSubScores(input: SubScoreInput): SubScores {
+	const { tagRepeats, ingredientOverlaps, easy, medium, hard } = input;
+
+	const proteinRepeats = tagRepeats.filter((t) => t.tagType === 'protein').length;
+	const ingredientOverlapCount = ingredientOverlaps.length;
+	const total = easy + medium + hard;
+
+	const effortBalance =
+		total === 0
+			? 10
+			: Math.min(10, Math.round(Math.max(0, 10 - Math.abs(easy - hard) * 1.5)));
+
+	return {
+		proteinDiversity: Math.max(0, Math.round(10 - proteinRepeats * 2)),
+		ingredientOverlap: Math.max(0, Math.round(10 - ingredientOverlapCount * 1.5)),
+		effortBalance
+	};
+}
+
+interface WarningInput {
+	tagRepeats: TagRepeat[];
+	ingredientOverlaps: IngredientOverlap[];
+	duplicatesInPlan: string[];
+}
+
+export interface Warning {
+	title: string;
+	explanation: string;
+}
+
+export function computeWarnings(input: WarningInput): Warning[] {
+	const { tagRepeats, ingredientOverlaps, duplicatesInPlan } = input;
+	const result: Warning[] = [];
+
+	for (const repeat of tagRepeats) {
+		if ((repeat.days?.length ?? 0) > 1) {
+			const days = (repeat.days ?? []).join(', ');
+			result.push({
+				title: `${repeat.tagName} mehrfach diese Woche`,
+				explanation: `${days} — erwäge einen Tausch für mehr Protein-Abwechslung.`
+			});
+		}
+	}
+
+	for (const overlap of ingredientOverlaps) {
+		if ((overlap.days?.length ?? 0) > 1) {
+			const days = (overlap.days ?? []).join(', ');
+			result.push({
+				title: `${overlap.ingredientName} in mehreren Gerichten`,
+				explanation: `${days} — sorge für Zutaten-Abwechslung.`
+			});
+		}
+	}
+
+	for (const name of duplicatesInPlan) {
+		result.push({
+			title: `${name} doppelt geplant`,
+			explanation: 'Dasselbe Rezept erscheint mehrfach — tausche eines aus.'
+		});
+	}
+
+	return result;
+}