[M4] TextFrame: scrollTo focused node when selection changes externally

[Korede-TA]

Goal

When a node is focused via click in SemanticFrame, MapFrame, Timeline etc., the TextFrame should automatically scroll to that node's text position — both in normal mode and in pinned comparison mode.

What to do

• Add data-node-id attributes to each rendered chunk/annotation span in TextFrame
• On selectionStore.focused change: document.querySelector([data-node-id="${focused}"])?.scrollIntoView({ behavior: 'smooth', block: 'nearest' })
• For documents (parent nodes): scroll to the document heading
• Smooth scroll, not instant jump
• If the focused node is not in the current TextFrame's scope (e.g. wrong pinned doc), do nothing

Acceptance criteria

• Clicking a chunk on the map scrolls TextFrame to that chunk's text
• Works in both pinned and unpinned mode
• No jarring instant jumps