Add skip idle playback option

[paulsmith]

Summary

• Add skip-idle playback mode that skips long inactive gaps while preserving action, network, console, DOM snapshot, event, screenshot, group, and timeline activity.
• Expose Skip idle controls in the main desktop and mobile player UI, plus a shared toggle in Compare mode.
• Add regression and UI coverage for skip math, DOM snapshot activity, mobile controls, and Compare mode.

Test Plan

• npm test
• npm run build
• Browser smoke: desktop and mobile Skip idle toggle visibility and aria-pressed behavior

Notes

• npm run lint still fails on existing scaffold lint issues outside this change: src/components/ui/command.tsx, src/components/ui/textarea.tsx, and tailwind.config.ts.

[paulsmith]

Screenshot of the new Skip idle playback toggle enabled in the Record Player toolbar.