#4327 docs: slim scroll clip authority ADR

Summary

Slim ADR 0026 to the scroll ownership decision and remove stale implementation paths. One file; no scope expansion. Part of #4205.

Migration ledger

• Status: kept shipped ownership and both open #2754 obligations; removed rollout history.
• Rules at a glance and contracts: kept ownership, same-frame, band, evidence, eligibility, macOS, and ejection contracts in the ADR. Removed file maps and incident detail; no contracts moved.
• Refuted alternatives: kept each alternative and its reason; removed site inventory and test paths.
• Consequences and open evidence: kept under-clipping risk, inventory prerequisite, and unexplained count; removed capture and fixture history.

Wording drift

The parent and same-frame rules retain the frame-change stop and smaller-host exceptions. The band authorization and keyboard scope retain their original limits. The synchronized iOS lists retain all six types; macOS scrollarea remains excluded with both eligibility outcomes. Typed ejection remains an unshipped internal obligation. The differential remains incomplete at runner stage. No modality change is intended.

Validation

Head: b31fb0b99ac86ff84f2556e37dd96fc96a111d09. Install, build, format, docs-prose, docs-links, and agent-guidance passed. Affected checks selected zero and passed with exactCommit=true, checkoutChanged=false (receipt .tmp/validation/run-h8qiRh/receipt.json). Runtime tests do not apply to this docs-only change. Hosted CI and the coordinator's independent sentence review remain pending.

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