docs(adr-0011): note offscreen live-rescue resolves the same surface as the tree #2452

Follow-up to #2438 / #2448.

Purpose. With in-place system-surface serving (#2448), the offscreen guarantee's live rescue (confirmOffscreenTargetVisible, which runs the direct querySelector) resolves the same surface as the tree under check, because prepareActiveCommandContext sets one activeApp for both. Record this in the guarantee matrix so the cell's rationale stays accurate.

Required behavior. Update the offscreen cell comment in packages/contracts/src/interaction-guarantees.ts (ADR 0011) to state the tree and the direct-selector rescue resolve the same surface.

Observable completion. Comment updated; no behavior change; honesty-gate stays green.

Dependencies. #2448.