Add database setup script and fix dark mode visibility

- Add scripts/setup-db.ts to programmatically create missing PocketBase
  collections (period_logs, dailyLogs) with proper relation fields
- Fix dark mode visibility across settings, login, calendar, and dashboard
  components by using semantic CSS tokens and dark: variants
- Add db:setup npm script and document usage in AGENTS.md
- Update vitest config to include scripts directory tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/layout.tsx

@@ -32,7 +32,7 @@ export default function RootLayout({
       >
         <a
           href="#main-content"
-          className="sr-only focus:not-sr-only focus:absolute focus:top-4 focus:left-4 focus:z-50 focus:bg-white focus:px-4 focus:py-2 focus:rounded focus:shadow-lg focus:text-blue-600 focus:underline"
+          className="sr-only focus:not-sr-only focus:absolute focus:top-4 focus:left-4 focus:z-50 focus:bg-background focus:px-4 focus:py-2 focus:rounded focus:shadow-lg focus:text-blue-600 dark:focus:text-blue-400 focus:underline focus:border focus:border-input"
         >
           Skip to main content
         </a>