fix: writing assistant live region scope

[web3blind]

Summary

• Remove aria-live="polite" from the entire writing assistant panel.
• Scope polite live announcements to the suggestions container only.
• Add a small regression test for the live-region markup.

Accessibility impact

The panel updates while users type. Making the whole panel a live region can cause screen readers to announce unrelated changes such as tone, stats, and server status repeatedly. This keeps announcements focused on writing suggestions instead of every panel update.

Fixes #14.

Tests

• npm test

[Aster1630]

The core change here is exactly right — scoping aria-live to #mt-suggestions instead of the whole panel will cut down on the noise a lot. The test approach (reading the source file and asserting on the HTML string) is lightweight and fits the existing pattern in this test suite well.

One thing worth considering before this merges: the Grammar & Spelling section (#mt-lt-issues and #mt-lt-state) also updates dynamically — when a server check completes, the issues list gets rewritten and the status message ("Checking grammar…", "Server unavailable", etc.) changes. Neither of those elements has a live region right now. For a keyboard/screen reader user who triggered the analysis, they'll get the suggestions announced but hear nothing when the grammar check resolves.

Probably the right move is aria-live="polite" on #mt-lt-issues or its wrapper #mt-lt-section, and a separate aria-live="assertive" (or at least polite) on #mt-lt-state for status messages — though polite is probably fine for both given the context. Whether that should be part of this PR or a follow-up is up to you, but it'd be worth an issue if it isn't tackled here since fixing half the live region problem is still a real improvement.

The change itself looks good to me — happy to see this land.

[Aster1630]

intregrated with PR #19