fix(web): allow reasoning scroll chaining

[teekalpha]

Summary

• allow wheel and touchpad scrolling to pass from the Reasoning panel to the chat viewport at the panel boundaries
• keep the existing 60vh height cap and internal scrolling from fix(web): reasoning overflow and settings label spacing #1166

Testing

• bun typecheck
• bun run test:web

[github-actions]

Findings

• No findings.

Questions

• None.

Summary

• Review mode: initial. No issues found in the added/modified line. Removing overscroll-contain restores default scroll chaining from the nested reasoning panel to the chat viewport; the outer .app-scroll-y still contains page-level overscroll via web/src/index.css:313.
• Residual risk: browser-specific wheel, touchpad, and touch boundary behavior is not covered by the repository’s unit tests.

Testing

• Not run (automation). GitHub test check was pending at review time; the PR reports bun typecheck and bun run test:web.

HAPI Bot