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.

WeChatDecrypt.spec

@@ -0,0 +1,45 @@
+# -*- mode: python ; coding: utf-8 -*-
+from PyInstaller.utils.hooks import collect_all
+
+datas = [('main.py', '.'), ('config.py', '.'), ('decrypt_db.py', '.'), ('export_messages.py', '.'), ('voice_to_mp3.py', '.'), ('find_all_keys.py', '.'), ('find_all_keys_windows.py', '.'), ('find_all_keys_linux.py', '.'), ('key_scan_common.py', '.'), ('key_utils.py', '.'), ('decode_image.py', '.'), ('find_image_key.py', '.'), ('find_image_key_monitor.py', '.'), ('monitor.py', '.'), ('monitor_web.py', '.'), ('mcp_server.py', '.'), ('config.example.json', '.')]
+binaries = []
+hiddenimports = []
+tmp_ret = collect_all('pilk')
+datas += tmp_ret[0]; binaries += tmp_ret[1]; hiddenimports += tmp_ret[2]
+
+
+a = Analysis(
+    ['app_gui.py'],
+    pathex=[],
+    binaries=binaries,
+    datas=datas,
+    hiddenimports=hiddenimports,
+    hookspath=[],
+    hooksconfig={},
+    runtime_hooks=[],
+    excludes=[],
+    noarchive=False,
+    optimize=0,
+)
+pyz = PYZ(a.pure)
+
+exe = EXE(
+    pyz,
+    a.scripts,
+    a.binaries,
+    a.datas,
+    [],
+    name='WeChatDecrypt',
+    debug=False,
+    bootloader_ignore_signals=False,
+    strip=False,
+    upx=True,
+    upx_exclude=[],
+    runtime_tmpdir=None,
+    console=True,
+    disable_windowed_traceback=False,
+    argv_emulation=False,
+    target_arch=None,
+    codesign_identity=None,
+    entitlements_file=None,
+)