First slice of #712 (dashboard SPA frontend → docs/). Shrinks the
buildAgentTree + treePrefixDom comment blocks in tabs.js to one-line
docs/ references; adds a new 'Topology tree' subsection to
docs/web-ui.md under '### Container row' carrying the substantive
prose.
Net effect on this region:
- 6 #NNN tracking cookies dropped (#363, #361, #388)
- 30 lines of substantive design comments collapsed to 6 lines of
references in tabs.js
- 35 new lines in docs/web-ui.md (the migrated prose, restructured
into a single coherent subsection rather than two adjacent comment
blocks)
- functional code unchanged; build clean
Deliberately small pattern-check (one cohesive subsystem) before
expanding to the rest of #712 (~140 more refs across tabs.js +
dashboard.css + index.html + common.js + flow.js). Reviewers can
sanity-check the shape (where prose lands, how short the in-code
ref becomes, whether section nesting reads well) before I scale.
refs #712