refactor: deslop — remove dead botanica preset, extract shared helpers

- Remove dead  theme preset (no CSS, not in DevToolbar)
- Extract  from closure → module-level export in lib/config/index.ts
- Extract  helper in app/[...path]/page.tsx to deduplicate password gate check
- Extract  inner component in app/page.tsx (was 4× inline in minimal/fullbleed/mosaic/split)
- Add 8 unit tests for buildSubpageGrid covering undefined, subset fields, layout fallback, and all fields

lib/__tests__/config.test.ts

@@ -12,7 +12,7 @@ vi.mock('@/lib/env', () => ({
   },
 }));
 
-import { slugify } from '@/lib/config';
+import { slugify, buildSubpageGrid } from '@/lib/config';
 
 describe('slugify', () => {
   it('converts a simple name to lowercase with hyphens', () => {
@@ -51,3 +51,50 @@ describe('slugify', () => {
     expect(slugify('Album 2024')).toBe('album-2024');
   });
 });
+
+describe('buildSubpageGrid', () => {
+  it('returns empty object when called without arguments', () => {
+    expect(buildSubpageGrid()).toEqual({});
+  });
+
+  it('returns empty object when called with undefined', () => {
+    expect(buildSubpageGrid(undefined)).toEqual({});
+  });
+
+  it('maps columns and gap correctly', () => {
+    expect(buildSubpageGrid({ columns: 4, gap: 8 })).toEqual({
+      grid: { columns: 4, gap: 8 },
+    });
+  });
+
+  it('maps aspectRatio correctly', () => {
+    expect(buildSubpageGrid({ aspectRatio: '16/9' })).toEqual({
+      grid: { aspectRatio: '16/9' },
+    });
+  });
+
+  it('preserves a valid layout value', () => {
+    expect(buildSubpageGrid({ layout: 'uniform' })).toEqual({
+      grid: { layout: 'uniform' },
+    });
+  });
+
+  it('falls back to masonry for an unknown layout', () => {
+    expect(buildSubpageGrid({ layout: 'unknown-layout' })).toEqual({
+      grid: { layout: 'masonry' },
+    });
+  });
+
+  it('omits fields that are not supplied', () => {
+    const result = buildSubpageGrid({ columns: 2 });
+    expect(result).toEqual({ grid: { columns: 2 } });
+    expect((result as { grid: object }).grid).not.toHaveProperty('gap');
+    expect((result as { grid: object }).grid).not.toHaveProperty('layout');
+  });
+
+  it('handles all fields together', () => {
+    expect(
+      buildSubpageGrid({ columns: 3, gap: 16, aspectRatio: '1', layout: 'masonry' }),
+    ).toEqual({ grid: { columns: 3, gap: 16, aspectRatio: '1', layout: 'masonry' } });
+  });
+});