Release v0.2.0

Sound Preview

• In-app playback before export (Preview / Stop Preview)
• Playback position header (current time / total)
• Playhead (cyan line) on spectrogram image during playback

Target Duration

• Optional "Set target duration" (0.5–600 s)
• Image is time-resampled so output length matches the specified duration

App Icon

• Custom app icon (docs/app-icon.png); macOS builds .icns at build time
• Windows: use resources/img2spec.ico (from same PNG) for exe icon

Documentation

• Japanese README (README_JP.md); link at top of README.md
• Docs updated for preview, duration, and troubleshooting