refactor(admin-book): rename Result to ApiResult and tighten return types

- Replace `Result` with `ApiResult` across admin book/borrow modules
- Change return type from `Result<Any?>` to `ApiResult<String>`
- Reformat multi-arg log statements for readability

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

@@ -6,7 +6,7 @@ import com.msksbr.bookmgr.dto.BookAddDto
 import com.msksbr.bookmgr.dto.BookUpdateDto
 import com.msksbr.bookmgr.script.log
 import com.msksbr.bookmgr.service.AdminBookService
-import com.msksbr.bookmgr.template.Result
+import com.msksbr.bookmgr.template.ApiResult
 import jakarta.servlet.http.HttpServletRequest
 import jakarta.validation.Valid
 import org.springframework.web.bind.annotation.*
@@ -35,8 +35,13 @@ class AdminBookController(private val adminBookService: AdminBookService, privat
         bookAddDto: BookAddDto,
         request: HttpServletRequest,
         @RequestAttribute(required = false) username: String?
-    ): Result<Any?> {
-        log.info("[AdminBook] add: user={}, name={}, author={}", username ?: "guest", bookAddDto.name, bookAddDto.author)
+    ): ApiResult<String> {
+        log.info(
+            "[AdminBook] add: user={}, name={}, author={}",
+            username ?: "guest",
+            bookAddDto.name,
+            bookAddDto.author
+        )
         log.info("[AdminBook] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
         return adminBookService.addBook(bookAddDto)
     }
@@ -50,7 +55,7 @@ class AdminBookController(private val adminBookService: AdminBookService, privat
         bookUpdateDto: BookUpdateDto,
         request: HttpServletRequest,
         @RequestAttribute(required = false) username: String?
-    ): Result<Any?> {
+    ): ApiResult<String> {
         log.info("[AdminBook] update: user={}, id={}", username ?: "guest", id)
         log.info("[AdminBook] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
         return adminBookService.updateBook(id, bookUpdateDto)
@@ -62,7 +67,7 @@ class AdminBookController(private val adminBookService: AdminBookService, privat
         id: Long,
         request: HttpServletRequest,
         @RequestAttribute(required = false) username: String?
-    ): Result<Any?> {
+    ): ApiResult<String> {
         log.info("[AdminBook] delete: user={}, id={}", username ?: "guest", id)
         log.info("[AdminBook] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
         return adminBookService.deleteBook(id)
@@ -75,7 +80,7 @@ class AdminBookController(private val adminBookService: AdminBookService, privat
         stock: Int,
         request: HttpServletRequest,
         @RequestAttribute(required = false) username: String?
-    ): Result<Any?> {
+    ): ApiResult<String> {
         log.info("[AdminBook] updateStock: user={}, id={}, stock={}", username ?: "guest", id, stock)
         log.info("[AdminBook] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
         return adminBookService.updateStock(id, stock)