Add SNS/image export and GUI contact export

Introduce SNS (朋友圈) and batch image tooling and enhance the GUI export workflow. Added new scripts: decrypt_sns.py (decrypt WeChat SNS cache) and batch_decrypt_images.py (bulk .dat image decrypt). Update build scripts and PyInstaller spec to include the new files. app_gui.py: add contact discovery, contact selection/export options dialog, new buttons (find image key, SNS), orchestrate combined export/voice/SNS tasks via subprocesses and env flags, and auto-run export after decryption. config.py: add output_base_dir, auto-detect WeChat Files path, and expose msgattach/xwechat cache dirs. export_messages.py: switch to output_base_dir, add image resource lookup and .dat locating/decryption helpers, and support environment-driven contact/format/image filters. Misc: update build.bat and packaging datas to include the new modules.

Co-Authored-By: Copilot <198982749+Copilot@users.noreply.github.com>

build.bat

@@ -29,6 +29,8 @@ pyinstaller --noconfirm --onefile --console --name "WeChatDecrypt" ^
     --add-data "decode_image.py;." ^
     --add-data "find_image_key.py;." ^
     --add-data "find_image_key_monitor.py;." ^
+    --add-data "decrypt_sns.py;." ^
+    --add-data "export_sns.py;." ^
     --add-data "monitor.py;." ^
     --add-data "monitor_web.py;." ^
     --add-data "mcp_server.py;." ^