feat(books): add book search service and improve error responses

- Add BookService interface and MyBatis-based implementation with fuzzy search
  by title or author
- Add forbidden (403) response helper to Result template
- Upgrade auth failure log from info to warn level
- Reorganize BookController imports and restructure class

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

@@ -61,7 +61,7 @@ class AuthController(
                 )
             )
         } else {
-            log.info("[Auth] login failed: user={}", loginDTO.username)
+            log.warn("[Auth] login failed: user={}", loginDTO.username)
             Result.error("Incorrect username or password")
         }
     }

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

@@ -1,5 +1,13 @@
 package com.msksbr.bookmgr.controller
 
+import com.msksbr.bookmgr.config.IpExtractor
+import com.msksbr.bookmgr.script.log
+import com.msksbr.bookmgr.service.BookService
+import com.msksbr.bookmgr.template.Result
+import jakarta.servlet.http.HttpServletRequest
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.RequestAttribute
+import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.RestController
 
 /*
@@ -7,9 +15,20 @@ import org.springframework.web.bind.annotation.RestController
 * 路径前缀（待定）：/api/books
 *
 * 计划接口：
-*   - 图书列表查询（支持分页、搜索）
+*   - 图书列表查询（搜索）
 *   - 单本图书详情
 */
 @RestController
-class BookController {
+@RequestMapping("/api/books")
+class BookController(private val bookService: BookService, private val ipExtractor: IpExtractor) {
+    @GetMapping("/search")
+    fun searchBook(
+        @RequestAttribute(required = false) username: String?,
+        query: String,
+        request: HttpServletRequest
+    ): Result<Any?> {
+        log.info("[Book] search: user={}, query={}", username ?: "guest", query)
+        log.info("[Book] user agent: {}, ip={}", request.getHeader("User-Agent"), ipExtractor.getRealIp(request))
+        return bookService.searchBook(query)
+    }
 }

src/main/kotlin/com/msksbr/bookmgr/service/BookService.kt

@@ -0,0 +1,16 @@
+package com.msksbr.bookmgr.service
+
+import com.msksbr.bookmgr.template.Result
+
+/*
+* 图书服务接口
+* 定义图书搜索逻辑的契约
+*/
+interface BookService {
+    /*
+    * 按书名或作者搜索图书
+    * @param query 搜索关键词，不可为空
+    * @return 搜索结果列表，无匹配时返回 404
+    */
+    fun searchBook(query: String): Result<Any?>
+}

src/main/kotlin/com/msksbr/bookmgr/service/impl/BookServiceImpl.kt

@@ -0,0 +1,35 @@
+package com.msksbr.bookmgr.service.impl
+
+import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper
+import com.msksbr.bookmgr.entity.Book
+import com.msksbr.bookmgr.mapper.BookMapper
+import com.msksbr.bookmgr.script.log
+import com.msksbr.bookmgr.service.BookService
+import org.springframework.stereotype.Service
+import com.msksbr.bookmgr.template.Result
+
+/*
+* 图书服务实现
+* 提供图书搜索功能，按书名或作者进行模糊匹配
+*/
+@Service
+class BookServiceImpl(private val bookMapper: BookMapper) : BookService {
+    override fun searchBook(query: String): Result<Any?> {
+        if (query.isBlank()) {
+            log.warn("[Book] search: query is blank")
+            return Result.error("Search query cannot be empty")
+        }
+        val result = bookMapper.selectList(
+            QueryWrapper<Book>()
+                .like("name", query)
+                .or()
+                .like("author", query)
+        )
+        if (result.isEmpty()) {
+            log.info("[Book] search: no results for {}", query)
+            return Result.notFound("No matching books found")
+        }
+        log.info("[Book] search: found {} results for {}", result.size, query)
+        return Result.success(result)
+    }
+}

src/main/kotlin/com/msksbr/bookmgr/template/Result.kt

@@ -53,10 +53,6 @@ data class Result<T>(
         *
         * JSON 输出示例：{ "code": 401, "message": "xxx" }
         */
-        /*
-        * 未登录响应 — 返回 401
-        * JSON 输出示例：{"code":401,"message":"Missing Authorization header"}
-        */
         fun unauthorized(message: String): Result<Any?> {
             return Result(
                 code = 401,
@@ -76,5 +72,19 @@ data class Result<T>(
                 data = null
             )
         }
+
+        /*
+        * 未找到响应 — 返回 404 + 自定义提示
+        * @param message 提示信息，如 "No matching books found"
+        *
+        * JSON 输出示例：{ "code": 404, "message": "xxx" }
+        */
+        fun notFound(message: String): Result<Any?> {
+            return Result(
+                code = 404,
+                message = message,
+                data = null
+            )
+        }
     }
 }