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/WeekStrip.test.ts

@@ -41,6 +41,13 @@ describe('WeekStrip', () => {
 		expect(dot.getAttribute('data-has-meal')).toBe('false');
 	});
 
+	it('when today equals selected day, both data-today and data-selected are true', () => {
+		render(WeekStrip, { props: { weekStart, slots, selectedDay: '2026-04-03', today: '2026-04-03' } });
+		const chip = screen.getByTestId('day-chip-2026-04-03');
+		expect(chip.getAttribute('data-today')).toBe('true');
+		expect(chip.getAttribute('data-selected')).toBe('true');
+	});
+
 	it('calls onselectDay callback when chip is clicked', async () => {
 		let emitted: string | null = null;
 		render(WeekStrip, {