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.
