Migrate build system from Maven to Gradle

Replaced Maven with Gradle by introducing a Gradle build structure, updating dependencies, and configuration files. Additionally, refactored package structure from `tech.ailef` to `space.mori.dalbodeule` for consistency.

build.gradle.kts

@@ -0,0 +1,72 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This project uses @Incubating APIs which are subject to change.
+ */
+
+plugins {
+    `java-library`
+    `maven-publish`
+    id("co.uzzu.dotenv.gradle") version "4.0.0"
+}
+
+repositories {
+    mavenLocal()
+    maven {
+        url = uri("https://repo.maven.apache.org/maven2/")
+    }
+}
+
+publishing {
+    repositories {
+        maven {
+            name = "Gitea"
+            url = uri(
+                "https://git.mori.space/api/packages/${env.GITEA_USERNAME.value}/maven"
+            )
+
+            credentials(HttpHeaderCredentials::class) {
+                name = "Authorization"
+                value = "token ${env.GITEA_TOKEN.value}"
+            }
+
+            authentication {
+                create<HttpHeaderAuthentication>("header")
+            }
+        }
+    }
+}
+
+dependencies {
+    api(libs.org.apache.poi.poi)
+    api(libs.org.apache.poi.poi.ooxml)
+    api(libs.org.apache.tika.tika.core)
+    api(libs.org.springframework.boot.spring.boot.starter.data.jpa)
+    api(libs.org.springframework.boot.spring.boot.starter.thymeleaf)
+    api(libs.org.springframework.boot.spring.boot.starter.jdbc)
+    api(libs.com.h2database.h2)
+    api(libs.org.apache.commons.commons.csv)
+    api(libs.org.springframework.boot.spring.boot.starter.validation)
+    api(libs.org.springframework.boot.spring.boot.starter.web)
+    api(libs.org.springframework.boot.spring.boot.configuration.processor)
+    testImplementation(libs.org.springframework.boot.spring.boot.starter.test)
+}
+
+group = "space.mori.dalbodeule"
+version = "0.4.1"
+description = "SnapAdmin"
+java.sourceCompatibility = JavaVersion.VERSION_17
+
+publishing {
+    publications.create<MavenPublication>("maven") {
+        from(components["java"])
+    }
+}
+
+tasks.withType<JavaCompile>() {
+    options.encoding = "UTF-8"
+}
+
+tasks.withType<Javadoc>() {
+    options.encoding = "UTF-8"
+}