Construct compact zones from measured geometry

[ivanmkc]

Summary

• extend authoritative painted-DOM construction from tiers to compact zones
• size parents from exact member and group-label bounds with shared 24px/32px spacing contracts
• pack disjoint parents using exact super-node dimensions and route labeled edges from explicit face-center anchors
• preserve loose-node handling and lanes-over-tiers precedence
• remove four compact-zone boards from the known-overlap ledger

Visual evidence

Before (gallery baseline):

After (this branch):

Verification

• full workspace suite: 1,057 passed, 18 skipped
• 32-board variety sweep: 31/32 clean, 1 unrelated known-bad, 0 regressions
• data-lineage, ETL, Kubernetes, infrastructure, and long-label grouped charts clean
• dedicated production-browser zone contract repeated: no overlap/spillout, standard padding, exact anchors, no edge-over-node crossings
• viewer production build

Stack

Depends on #306. Swimlanes follow as a separate stacked PR.