Add EXE build support and frozen-runtime path handling

[ryo08271154]

Motivation

• Make it possible to build and distribute Windows executables and ensure config/plugins/cookie files are resolved correctly when the application runs as a frozen .exe.
• Avoid plugin discovery and file-path issues that commonly occur after packaging with PyInstaller by centralizing runtime path resolution.

Description

• Added app_paths.py which provides get_app_dir(), get_resource_dir() and ensure_config_dir() to resolve write/read paths consistently for normal and frozen execution.
• Added build_exe.py to build GUI (control.py) and CUI (voice_control.py) distributions using PyInstaller and to collect plugin modules as hidden imports via pkgutil.
• Updated core modules to use get_app_dir()/ensure_config_dir() so voice_control.py, control.py and edit_config.py load and write config/ next to the executable at runtime.
• Switched plugin discovery/loading to pkgutil.iter_modules() in plugin.py and adjusted plugins (plugins/switchbot.py, plugins/watchlist.py) to use app_paths for config/cookie file paths.
• Documented the EXE build/run steps in README.md and added pyinstaller to requirements.txt.

Testing

• Compiled key files with python -m py_compile app_paths.py build_exe.py voice_control.py control.py plugin.py edit_config.py plugins/watchlist.py plugins/switchbot.py, which completed successfully.

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Codex Task