#23136 Revert "Agent chat: the bottom stack is a no-scroll zone"

Summary

Takes back #22819: it merged at ef6e1b2cf7ec without no SHIP review receipt on the head.

Opened by merge-audit (leo-workspace tools/merge_audit.py), which never merges it. To keep #22819 instead, add the missing evidence for ef6e1b2cf7ec on #22819 (an independent review's Review (subagent, correctness first): SHIP at <head> comment, a green compile, a risk tier; for a compile the router skipped, land-now from a maintainer); the next audit pass then closes this PR. Otherwise review and land it.

Changelog

none

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Summary by cubic

Reverts #22819, so the agent chat pane's bottom stack (composer, questions, notices, queue) is no longer a no-scroll zone. A wheel or trackpad scroll over those parts now scrolls the transcript again, as in the Claude and Codex apps; parts that scroll themselves (a long prompt, the queue, a menu) keep the wheel at their ends. Removes the overscroll-behavior: contain rule and the composer's no-scroll special case, and updates the pass-through tests.