[Improvement]: A11y — aria-live regions for chat streaming, toasts, updater and git feedback

[matiaspalmac]

Describe the improvement

Dynamic state changes are invisible to screen readers:

• Chat streaming output in apps/desktop/src/addons/builtin.ai-assistant/AiChatComponent.tsx:702-813 is not announced.
• Updater state transitions in apps/desktop/src/components/UpdaterDialog.tsx:182-313 appear without a live region.
• flash() git feedback in apps/desktop/src/addons/builtin.git-explorer/GitExplorerComponent.tsx:414-418 updates silently.
• MarketplaceView uses alert() (disruptive) instead of accessible toasts.

Proposed change:

1. Wrap dynamic chat content in <div role="log" aria-live="polite" aria-busy={isStreaming}>.
2. Wrap updater, git feedback and toasts in role="status" aria-live="polite" for informational and role="alert" aria-live="assertive" for errors.
3. Replace alert() with an accessible toast component.

Would you like to implement this improvement yourself by sending a PR?

Maybe