Adds 07-UI-SPEC.md for Phase 7 (Mobile Test Harness). Documents the
assertable mobile-UI quality bar the harness enforces: touch-target
thresholds (≥44px), no-horizontal-overflow rule, two-profile viewport
matrix (iPhone 14/WebKit + Pixel 7/Chromium), role-based accessible name
requirements, empty/error-state copy anchors, screenshot omission rationale,
and CI portability rules. Locks D-01 through D-10 from CONTEXT.md as the
assertion contract.
Lucas Berger
179766d447