Standardize grouped edge guide rhythm

[ivanmkc]

Summary

• center unequal measured members within logical ranks
• route grouped edges over deterministic 8 px guides with 16 px stubs, doglegs, and parallel-track pitch
• consolidate exact shared terminal trunks while keeping unrelated tracks separated
• align cross-zone anchors to the declared rank axis so typography cannot flip their semantics
• render round connector caps/joins and enforce the painted contract for tiers, zones, and swimlanes

This PR is stacked on #309 and advances #154.

Before / after

Architecture tiers

Before (#309)	After

Data-lineage zones

Before (#309)	After

Swimlanes

Before (#309)	After

Verification

• 5 focused unit files: 48/48 tests passed
• viewer TypeScript, server bundle, and client bundle passed
• painted browser E2E passed for tiers, zones, and swimlanes at 1440 × 1000
• live port 8080 deployment: 13 swimlane nodes, 13 edges, four lanes, no render error, all edge joins/caps round
• broad viewer run reached all geometry suites successfully; remaining failures reproduce existing host constraints around socket binding, invalid localStorage setup, and HTTP-server hooks, so CI remains required for those unrelated suites

The painted E2E rejects node/container overlap, padding spillout, anchor mismatch, node-crossing edges, unrelated coincident or sub-16 px parallel tracks, short interior doglegs, avoidable bends, and non-round path styling.