fix: allow scrolling the sent-to-prompt code attachment

[laileni-aws]

Problem

When code is added to the chat prompt via "Send to prompt" (right‑click → Amazon Q → Send to prompt, or the keyboard shortcut), the code snippet cannot be scrolled: long/wide code is clipped and the horizontal/vertical scrollbars are not usable, so the full code cannot be viewed — in both the inline prompt attachment and its hover preview.

Root cause

In src/styles/components/chat/_chat-prompt-attachment.scss, the snippet's syntax highlighter is styled with overflow: hidden (and pointer-events: none). On hover the inline attachment sets pointer-events: auto but keeps overflow: hidden, so there is never a usable scrollbar; the preview overlay inherits the same overflow: hidden.

Fix

• Inline attachment: on :hover, set overflow: auto on the syntax highlighter so the (already interactive) snippet can be scrolled to view the full code.
• Preview overlay (.mynah-prompt-input-snippet-attachment-overlay): set overflow: auto and pointer-events: auto on the syntax highlighter so the preview scrolls and is interactive.

Scope / testing

• Change is limited to the prompt code‑attachment styles; the default (non‑hover) inline rendering keeps overflow: hidden, so it is visually unchanged.
• npm run build compiles the styles; full unit suite, eslint, and prettier --check pass. No end‑to‑end snapshot covers the hover/overlay state.
• CSS‑only presentation change that I could not render in a live IDE from this environment; a quick visual sign‑off (scroll a long snippet + its preview) is recommended before marking ready.

Additional change

• ui-tests/__test__/flows/quick-action-commands-header.ts: coerced a Playwright evaluate result to a boolean to satisfy @typescript-eslint/strict-boolean-expressions and keep the repo lint gate green.