feat(api): add controller layer and auth service stubs

- Add AdminBookController, AdminBorrowController, BookController,
  BorrowController, and DashBoardController stubs
- Implement AuthController with login endpoint
- Add AuthService interface and AuthServiceImpl stub

src/main/kotlin/com/msksbr/bookmgr/controller/AdminBookController.kt

@@ -0,0 +1,7 @@
+package com.msksbr.bookmgr.controller
+
+import org.springframework.web.bind.annotation.RestController
+
+@RestController
+class AdminBookController {
+}