feat(ui): Terrakotta Nacht replaces Soft, smooth menus and sliding notes on phones

- dark counterpart of Terrakotta; Soft users move to it
- add tailwindcss-animate: the existing animate-in/fade/slide classes now
  run; menus zoom in, sheets slide up, notes slide in on phones
- no animations with reduced motion

chore(release): v0.13.0

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/__tests__/theme.test.ts

@@ -65,3 +65,21 @@ describe('custom themes', () => {
     expect(document.documentElement.classList.contains('dark')).toBe(true);
   });
 });
+
+describe('built-in themes', () => {
+  beforeEach(() => localStorage.clear());
+
+  it('moves removed themes to their successors', () => {
+    localStorage.setItem('mindsift_active_theme', 'soft');
+    expect(getActiveTheme()).toBe('terracotta-night');
+    localStorage.setItem('mindsift_active_theme', 'high-contrast');
+    expect(getActiveTheme()).toBe('dark');
+  });
+
+  it('treats Terrakotta as a light theme and Terrakotta Nacht as dark', () => {
+    setActiveTheme('terracotta');
+    expect(document.documentElement.classList.contains('dark')).toBe(false);
+    setActiveTheme('terracotta-night');
+    expect(document.documentElement.classList.contains('dark')).toBe(true);
+  });
+});