Release PlotMapper v1.2.0

[maxliebscher]

Summary

• Adds the optional multi-route workflow with route-level color, visibility, numbering, arrows, style, width, active route selection, and compatible project serialization.
• Updates presentation/focus behavior for v1.2.0: per-route reveal progress, nearby context-point reveal, route progress pills, and export parity for the new route visuals.
• Polishes the route toolbar, confirmed color picker, collapsible/menu opacity controls, Story Picker, point/helper sizing, Reader/Tutorial copy, offline-release checks, and README screenshot gallery.

Test Plan

• npm.cmd test
• npm.cmd run smoke
• npm.cmd run build
• git diff --cached --check before commit
• README screenshot gallery previewed locally with Playwright: 10-image gallery, no horizontal scroll, aligned 3-column grid

Notes

• Multi-Fog production behavior uses the tested "per route own progress" path from the demo; the older broader concept remains documented for later decisions.
• Release is intentionally isolated on this branch for deeper manual testing before merging to main.