Two threads cleaned up in tabs.js:
1. Top-of-file '#406 step 1/2/3' historical narrative deleted —
it documented past module splits (moves to common.js / flow.js,
file rename app.js → tabs.js) which are git-history concerns,
not current-behaviour docs. Replaced with a two-sentence
contract description that references docs/web-ui.md and the
present-tense module split.
2. Five 'moved to ./common.js (#406)' stubs deleted — same
reasoning. The imports at the top of the file already document
what's in common.js; standalone 'this function lives elsewhere'
pointers are noise once you stop tracking the move event.
paintAtomic's substantive rationale migrated to a new
'Atomic section repaint' subsection in docs/web-ui.md (under the
existing focus-preservation note); in-code comment shrinks to a
two-line reference. Same pattern as the topology-tree batch.
Net: 36 fewer lines in tabs.js, 14 new in docs/web-ui.md.
Functional code unchanged; build clean.
refs #712
711d42031c