fix: redundant/double scrollbar in bottom sheet (e.g. MCP view)

[laileni-aws]

Summary

The bottom sheet (used for panels such as the MCP view) always rendered a vertical scrollbar because its scroll containers used overflow-y: scroll. Combined with the inner scrollable list, this produced a redundant second scrollbar wrapping the whole panel (a "double scrollbar"), and left an empty scrollbar visible even when the content fit. This PR switches those containers to overflow-y: auto so a scrollbar only appears when the content actually overflows.

Problem

When opening a panel rendered in the sheet (for example the MCP view):

1. The sheet body (.mynah-sheet-body) has overflow-y: scroll, so it always shows a scrollbar.
2. Its content includes an inner scrollable list (.mynah-detailed-list, overflow-y: auto) that shows its own scrollbar when the list overflows.
3. The result is two vertical scrollbars on the right — one for the list content and a redundant one wrapping the entire panel — plus a permanently visible (often empty) scrollbar even when nothing overflows.

The fullscreen sheet variant (.mynah-sheet-fullscreen) had the same overflow-y: scroll, producing a permanent scrollbar as well.

Fix

In src/styles/components/_sheet.scss, change overflow-y: scroll to overflow-y: auto for both .mynah-sheet-body and .mynah-sheet-fullscreen.

auto renders the scrollbar only when the content exceeds the available height, so:

• the redundant outer scrollbar no longer appears alongside the inner list's scrollbar, and
• no empty scrollbar is shown when the content fits.

Testing

• npm run build compiles the styles successfully.
• Full unit test suite passes (npx jest): 842 tests.
• eslint and prettier --check pass.
• This is a CSS-only change; there are no existing end-to-end snapshots that capture the sheet, so no screenshot baselines are affected.

Additional change

• ui-tests/__test__/flows/quick-action-commands-header.ts: coerced the result of a Playwright evaluate call to a boolean with Boolean(...) before using it in a condition, satisfying @typescript-eslint/strict-boolean-expressions and keeping the repo lint gate green.

Notes

• Change is limited to sheet overflow styling; no public API or behavior changes beyond scrollbar visibility.