Expose an autoplay-policy control for the in-app Browser pane

What

Add a way to disable media autoplay in the Claude Code Desktop in-app Browser pane (the Cmd+Shift+B preview browser).

Why

Pages loaded in the Browser pane autoplay <video>/<audio> with sound. When a preview tab is left open in a background thread, it keeps playing audio with no obvious source — the pane doesn't surface which page/thread is making sound, so it's hard to trace and stop. It's also just unexpected for a dev-preview surface to autoplay media.

Proposal

Pass through Chromium's --autoplay-policy=user-gesture-required for the Browser pane, ideally behind a settings.json toggle (e.g. browser.autoplay: "user-gesture-required" | "allowed"), defaulting to gesture-required. A per-tab mute control in the pane UI would also help.

Environment

Claude Code Desktop (macOS).