Add Smooth Pause/Resume

[1-co]

An optional Smooth Pause/Resume feature that fades audio out on pause and back in on play. The current instant cut remains the default behavior.

How it works:

• Normal tap / left-click: Keeps the standard instant pause.
• Long-press / right-click: Triggers a smooth fade-out/fade-in.

Settings:

Configured via a toggle and a duration slider (1–12 seconds) in Playback Settings, using the exact same logic as the Crossfade timer.

Why it matters:

An instant audio cut kills the vibe when playing music for others. A smooth fade provides a seamless, professional DJ-like experience without suddenly dropping a room into silence, while keeping standard controls intact for everyday use.