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>

vitest.config.ts

@@ -13,7 +13,7 @@ export default defineConfig({
   },
   test: {
     environment: "jsdom",
-    include: ["src/**/*.test.{ts,tsx}"],
+    include: ["src/**/*.test.{ts,tsx}", "scripts/**/*.test.ts"],
     setupFiles: ["./src/test-setup.ts"],
   },
 });