The watch-based plumbing from iteration click to PDF scroll relied on a
"flip via null" pattern (assign null then the value) to coerce Vue into
re-firing the watcher. Vue 3 collapses synchronous mutations of the same
ref and only delivers the final value, so the trick was a no-op: a second
click on the same iteration left the document view stuck on the previous
page. The bug only showed when the trace had a single iteration — with
several, the user naturally clicks different ones and the value really
changes.
Replace the watch chain with imperative dispatch. ReasoningPanel now just
emits iterationFocus; ReasoningWorkspace handles it by calling the graph
focus and the new StructureViewer.scrollToFocused method directly. Both
side effects fire on every click regardless of state.
Propagate Docling `self_ref` through PageElement so bboxes and graph nodes
share a stable identity. Add a Document/Graph mode switch to the reasoning
workspace; selecting a node highlights its bbox (numbered badge, focus ring,
optional dim of non-visited) and clicking a bbox re-centers the graph.
