No mobile e2e coverage — every mobile regression passes CI today

[kmatzen]

No Playwright project, spec, or devices[…] context uses a mobile viewport — the whole suite runs desktop-sized Chromium. Every finding in the mobile audit (#125) passes CI today.

Worth adding:

• A mobile project (iPhone 13 + Pixel 5) covering the core path: enter the modeler, add a shape, edit a dimension, export.
• An assertion that no interactive element on a coarse-pointer viewport is under 44 px. That single check is what keeps the touch-target work from regressing.

Assessment: docs/mobile-audit/README.md §9 (#125).