feat(admin-borrows): add search endpoint replacing getAll

Replace the simple \"get all borrows\" endpoint with a search-based
approach supporting queries by book name, author, username, and role.

- Change endpoint from GET /getall to GET /search?query=xxx
- Add search service implementation using QueryWrapper with LIKE
  predicates across Book, User, and BorrowRecord tables
- Use kotlinx-coroutines for parallel async data fetching per result
- Add kotlinx-coroutines-core and kotlinx-coroutines-reactor deps

build.gradle.kts

@@ -22,6 +22,8 @@ repositories {
 dependencies {
     implementation("org.springframework.boot:spring-boot-starter")
     implementation("org.jetbrains.kotlin:kotlin-reflect")
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-reactor:1.10.2")
     implementation("org.springframework.boot:spring-boot-starter-web")
     implementation("org.aspectj:aspectjweaver")
     implementation("org.springframework.security:spring-security-crypto")