Fix permission and operator overlays not showing their choices on the landing screen

[TheGreatAxios]

Summary

• Fixes the landing-screen float asking for only one choice row of headroom instead of the overlay's real, already fraction-capped content height
• A permission approval or operator question that fires before the first transcript row (the landing screen) now gets its full computed box height, so every choice is on screen instead of the list being starved down to whatever the even top/bottom split happened to leave
• Adds a regression test asserting all choices of a multi-option operator question render on the landing screen

Verification

• bun run typecheck, bun run build, and bun test all pass (one pre-existing, unrelated flake in markdown-rows.test.ts around fenced-code timing, confirmed present on origin/main before this change)
• Drove the actual shell via the OpenTUI test harness (createAppShell + wireGates, real render passes, captured frames) with a realistic permission request (a run_shell call with one scope) at 80x24 and 120x40: before the fix, "Always allow npm install" — the one choice the operator actually needs to grant durable trust — was clipped off screen on the very first turn; after the fix, all three choices ("Reject", "Accept once", "Always allow npm install") render

Closes CL-5560

[linear-code]

CL-5560