Add GUI, packaging and export/voice tools

Introduce a tkinter GUI and tooling to produce a single executable and export/convert message data. Adds app_gui.py (GUI launcher that runs decrypt/export/voice subtasks), export_messages.py (export messages to CSV/HTML/JSON), voice_to_mp3.py (extract SILK_V3 voice blobs and convert to MP3 via pilk + ffmpeg), WeChatDecrypt.spec and build.bat (PyInstaller spec and convenience build script), and EXE_USAGE.md (usage for the standalone exe). Update config.py to detect the application base directory when packaged, update README.md to document the GUI and packaging flow, and add pilk/pyinstaller to requirements.txt. Also expand .gitignore with common IDE/build/temp patterns and add output/data directories to ignore. These changes enable one-file packaging and provide end-user tools for decrypting, exporting and converting audio.

build.bat

@@ -0,0 +1,53 @@
+@echo off
+chcp 65001 >nul
+echo ========================================
+echo   WeChatDecrypt 打包脚本
+echo ========================================
+echo.
+
+:: 检查 pyinstaller
+where pyinstaller >nul 2>&1
+if errorlevel 1 (
+    echo [!] 未找到 pyinstaller，正在安装...
+    pip install pyinstaller
+)
+
+echo [*] 开始打包...
+echo.
+
+pyinstaller --noconfirm --onefile --console --name "WeChatDecrypt" ^
+    --add-data "main.py;." ^
+    --add-data "config.py;." ^
+    --add-data "decrypt_db.py;." ^
+    --add-data "export_messages.py;." ^
+    --add-data "voice_to_mp3.py;." ^
+    --add-data "find_all_keys.py;." ^
+    --add-data "find_all_keys_windows.py;." ^
+    --add-data "find_all_keys_linux.py;." ^
+    --add-data "key_scan_common.py;." ^
+    --add-data "key_utils.py;." ^
+    --add-data "decode_image.py;." ^
+    --add-data "find_image_key.py;." ^
+    --add-data "find_image_key_monitor.py;." ^
+    --add-data "monitor.py;." ^
+    --add-data "monitor_web.py;." ^
+    --add-data "mcp_server.py;." ^
+    --add-data "config.example.json;." ^
+    --collect-all pilk ^
+    app_gui.py
+
+if errorlevel 1 (
+    echo.
+    echo [!] 打包失败
+    pause
+    exit /b 1
+)
+
+echo.
+echo ========================================
+echo   打包完成！
+echo   输出: dist\WeChatDecrypt.exe
+for %%F in (dist\WeChatDecrypt.exe) do echo   大小: %%~zF bytes
+echo ========================================
+echo.
+pause