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>

AGENTS.md

@@ -24,6 +24,19 @@ Run these after implementing to get immediate feedback:
 - Path aliases: `@/*` maps to `./src/*`
 - Pre-commit hooks: Biome lint + Vitest tests via Lefthook
 
+## Database Setup
+
+PocketBase requires these collections: `users`, `period_logs`, `dailyLogs`.
+
+To create missing collections:
+```bash
+POCKETBASE_ADMIN_EMAIL=admin@example.com \
+POCKETBASE_ADMIN_PASSWORD=yourpassword \
+pnpm db:setup
+```
+
+The script reads `NEXT_PUBLIC_POCKETBASE_URL` from your environment and creates any missing collections. It's safe to run multiple times - existing collections are skipped.
+
 ## Codebase Patterns
 
 - TDD required: Write tests before implementation