feat: add service type management module (#15)

- Add rlz_service_type and rlz_price_history tables
- Add backend entities, mapper, service, and controller for /system/serviceType
- Add frontend Vue page with list/create/edit/price update/price history
- Add sys_menu entries and role permissions for admin role
- Add admin backend module planning document

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "rlz"]
-	path = rlz
-	url = https://gitee.com/renjianbo0118/ruoyi.git