fix(planner): address all PR review blockers

- Fix logic bug `{#if !isPlanner === false}` - view/cook buttons now visible for all roles, swap only for planner
- Convert Tauschen from dead button to link with suggestions href
- Add week.ts unit tests (23 tests covering getWeekStart Sunday edge case, prevWeek/nextWeek, weekDays, isToday, formatWeekRange)
- Fix isToday to use UTC consistently (.toISOString().slice(0,10)) instead of local date
- Add server-side role guard to createPlan action (403 for members)
- Add weekStart format validation in createPlan action
- Add isSelected prop to DayMealCard with green treatment
- Make variety banner sticky on mobile (always visible per spec)
- Add day name abbreviation above date badge in desktop column headers
- Remove placeholder Navigation text from desktop sidebar
- Add aria-label to desktop empty tile buttons
- Add variety score partial failure test, multiple overlaps test, WeekStrip today+selected test

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

frontend/src/lib/planner/VarietyScoreCard.test.ts

@@ -53,4 +53,21 @@ describe('VarietyScoreCard', () => {
 		render(VarietyScoreCard, { props: { ...baseProps, score: 0 } });
 		expect(screen.getByText('0')).toBeTruthy();
 	});
+
+	it('renders multiple ingredient overlap warnings', () => {
+		render(VarietyScoreCard, {
+			props: {
+				...baseProps,
+				ingredientOverlaps: [
+					{ ingredientName: 'Tomate', days: ['2026-03-30', '2026-03-31'] },
+					{ ingredientName: 'Zwiebel', days: ['2026-03-30', '2026-04-01', '2026-04-02'] },
+					{ ingredientName: 'Knoblauch', days: ['2026-03-31', '2026-04-01'] }
+				]
+			}
+		});
+		expect(screen.getByText(/Tomate/)).toBeTruthy();
+		expect(screen.getByText(/Zwiebel/)).toBeTruthy();
+		expect(screen.getByText(/Knoblauch/)).toBeTruthy();
+		expect(screen.getByText(/3 Mahlzeiten/)).toBeTruthy();
+	});
 });