feat(system-admin): implement bootstrap for system admin promotion and enhance system settings management

- Added WEKNORA_BOOTSTRAP_SYSTEM_ADMIN_EMAIL environment variable to promote a specified user to system admin on startup.
- Introduced a new bootstrap process in `bootstrap.go` to handle the promotion logic.
- Updated `.env.example` to document the new environment variable and its behavior.
- Created new views for managing system administrators and system settings, including listing, promoting, and revoking admin privileges.
- Enhanced the frontend to reflect the new system admin features, including UI elements for admin management and settings configuration.
- Updated API interfaces to support system admin functionalities, ensuring proper data handling and user management.

migrations/versioned/000053_system_settings.down.sql

@@ -0,0 +1,6 @@
+-- Rollback: drop system_settings table
+DO $$ BEGIN RAISE NOTICE '[Migration 000053 DOWN] Dropping table: system_settings'; END $$;
+
+DROP TABLE IF EXISTS system_settings CASCADE;
+
+DO $$ BEGIN RAISE NOTICE '[Migration 000053 DOWN] Done.'; END $$;