fix(test-app): keep the inert surface control above the settings fold
Motivation
Adding the Snapshot depth section (#3786) pushed the Inert surface card into the band the iOS 26 floating tab bar covers on a 402x874 phone, so open-inert-surface stopped being visible after the Settings tab tap: agent-device refuses invisible targets, its differential legs went red every night since 10-18 (settle-after-tap step 5, tap-retry-if-no-change step 3), while Maestro's presence-based check kept passing.
Approach
The settle flow's own guard rejects an inserted scroll and pins the assert on this control, so the fixture restores the reachability the flows were written against: the inert card moves back to the second section, ahead of the growth that followed it. A comment on the section records the reachability constraint so later sections don't push it under the fold again.
Test evidence
Local snapshot before: the settings tree ended at Open accessory setup lab with [content below scroll-area hidden]; after: open-inert-surface resolves at (201, 609) and the tap navigates to the inert screen.
Replayed onto current main (6f5b86a65): check:affected selected 6 checks for this path — format and lint pass; test-app-typecheck is GitHub-authoritative (Test App Build Cache).