Fix transcript actions popover clipped by workspace sections

[wassgha]

Summary

The Cut / Correct / Speaker selection toolbar (and the Correct / Speaker pickers) were absolutely positioned inside the transcript scroller, so overflow clipping on the transcript pane could hide them behind the header or neighboring workspace sections.

Fix

• Anchor these menus to the selected word spans with Floating UI (strategy: "fixed" + flip/shift)
• Render them through FloatingPortal at document.body, matching the existing app menu pattern
• Track the selection live on scroll/resize via autoUpdate

Test plan

• Select words near the top of the transcript — toolbar fully visible (flips below when needed; not clipped by Transcript header)
• Open Correct and Speaker from the toolbar — both pickers escape transcript overflow
• Confirm toolbar is portaled with position: fixed ([data-transcript-toolbar] under document.body)
• Select words elsewhere in the transcript — toolbar remains fully on screen
• Cut / Restore / Correct / Speaker actions still apply edits as before

Screenshots