Feat: FTP 서버 기본 구조 구현

- AndroidManifest.xml에 필요한 권한 추가 (INTERNET, STORAGE 등)
- FTPResponse 클래스 생성: FTP 응답 코드 상수 정의
- FTPSession 클래스 생성: 개별 클라이언트 세션 처리
  * 명령어 읽기/응답 보내기 기본 루프
  * USER, PASS, QUIT, SYST, PWD, NOOP 명령어 처리
- FTPServer 클래스 생성: 메인 서버 로직
  * ServerSocket으로 포트 2121에서 수신 대기
  * ExecutorService로 다중 클라이언트 연결 관리
- FTPService 클래스 생성: 백그라운드 포그라운드 서비스
  * 서버 시작/중지 Intent 처리
  * 알림 채널 및 포그라운드 서비스 구현
- MainActivity UI 업데이트: 서버 제어 기능
  * 시작/중지 버튼 추가
  * 서버 상태 표시
  * 런타임 권한 요청 처리

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.idea/.gitignore

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+# Default ignored files
+/shelf/
+/workspace.xml

.idea/.name

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+Gyub_s Android FTP Server

.idea/AndroidProjectSystem.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AndroidProjectSystem">
+    <option name="providerId" value="com.android.tools.idea.GradleProjectSystem" />
+  </component>
+</project>

.idea/compiler.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <bytecodeTargetLevel target="11" />
+  </component>
+</project>

.idea/deploymentTargetSelector.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="deploymentTargetSelector">
+    <selectionStates>
+      <SelectionState runConfigName="app">
+        <option name="selectionMode" value="DROPDOWN" />
+      </SelectionState>
+    </selectionStates>
+  </component>
+</project>

.idea/gradle.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="testRunner" value="CHOOSE_PER_TEST" />
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleJvm" value="jbr-21" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+            <option value="$PROJECT_DIR$/app" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>

.idea/markdown.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MarkdownSettings">
+    <option name="previewPanelProviderInfo">
+      <ProviderInfo name="Compose (experimental)" className="com.intellij.markdown.compose.preview.ComposePanelProvider" />
+    </option>
+  </component>
+</project>

.idea/misc.xml

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+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="Android Studio default JDK" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/build/classes" />
+  </component>
+  <component name="ProjectType">
+    <option name="id" value="Android" />
+  </component>
+</project>

.idea/runConfigurations.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RunConfigurationProducerService">
+    <option name="ignoredProducers">
+      <set>
+        <option value="com.intellij.execution.junit.AbstractAllInDirectoryConfigurationProducer" />
+        <option value="com.intellij.execution.junit.AllInPackageConfigurationProducer" />
+        <option value="com.intellij.execution.junit.PatternConfigurationProducer" />
+        <option value="com.intellij.execution.junit.TestInClassConfigurationProducer" />
+        <option value="com.intellij.execution.junit.UniqueIdConfigurationProducer" />
+        <option value="com.intellij.execution.junit.testDiscovery.JUnitTestDiscoveryConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinJUnitRunConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinPatternConfigurationProducer" />
+      </set>
+    </option>
+  </component>
+</project>

.idea/vcs.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>