Line label backdrop styles on 3D measurement layerbar

[mxfh]

Summary

• rebases the annotation distance line label style work onto feat/03603-3d-measurement-geoportal-layerbar
• ports preview line label backdrop/text-echo visual options from the old runtime-v2 path into the current annotations runtime
• keeps the target branch story conflict side where it already had newer collision-resolution story wiring

Validation

• nx run annotations-runtime:build --output-style=stream
• nx run annotations-runtime:lint --output-style=stream
• nx run stories:lint --output-style=stream

Notes

• Created from feature/annotation-distance-line-label-styles, with conflicts resolved against feat/03603-3d-measurement-geoportal-layerbar.