Fix Vespers/Compline header to use evening day, not daytime day

day-nav.ts's header always resolved via resolveDay(date) regardless of
selected hour, so viewing Vespers/Compline on a day whose evening
anticipates tomorrow's First Vespers (e.g. Aug 25, 2026: St. Louis's day,
but St. Zephyrinus claims First Vespers per calendar/vespers.ts) still
showed today's saint in the header while the hour's actual content had
already switched to tomorrow's. Now uses resolveEveningDay for those two
hours specifically.

Also adds an explicit "First Vespers (of tomorrow)" / "Second Vespers (of
today)" status line to the Vespers header, via new
getVespersStatusLabel(), so the anticipation/commemoration result is
visible rather than only inferable from which saint's name shows up.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014axryJBrRswYh2niA7WCUc

tests/ui/shell.test.ts

@@ -41,6 +41,34 @@ describe('shell', () => {
     expect(root.querySelectorAll('.ordo-part-psalm').length).toBeGreaterThan(0);
   });
 
+  it('shows tomorrow\'s saint (not today\'s) in the header when Vespers/Compline anticipate First Vespers', () => {
+    // Live-verified case (calendar/vespers.ts): Aug 25, 2026 is St. Louis
+    // (Simplex), but St. Zephyrinus (Aug 26, also Simplex) claims First
+    // Vespers over him -- the evening's real identity is tomorrow's, not
+    // today's. The header previously always used the daytime `resolveDay`
+    // regardless of selected hour, so it kept showing St. Louis even while
+    // the hour content itself had already switched to St. Zephyrinus.
+    setDate('2026-08-25');
+    setSelectedHour('vespers');
+    window.history.replaceState(null, '', '/vu/2026-08-25/vespers');
+    const root = document.getElementById('app')!;
+    mountShell(root);
+
+    expect(root.querySelector('.day-nav-label')?.textContent).toContain('Zephyrinus');
+    expect(root.querySelector('.day-nav-label')?.textContent).not.toContain('Louis');
+    expect(root.querySelector('.day-nav-vespers-status')?.textContent).toContain('First Vespers');
+  });
+
+  it('shows a plain Second Vespers status when Vespers is not anticipating tomorrow', () => {
+    setDate('2026-08-09');
+    setSelectedHour('vespers');
+    window.history.replaceState(null, '', '/vu/2026-08-09/vespers');
+    const root = document.getElementById('app')!;
+    mountShell(root);
+
+    expect(root.querySelector('.day-nav-vespers-status')?.textContent).toContain('Second Vespers');
+  });
+
   it('switches to Matins and shows its real content, not the pending message', () => {
     const root = document.getElementById('app')!;
     mountShell(root);