Announce DocumentDB Local tree state transitions to screen readers

Problem

The DocumentDB Local row in the Connections view changes state on its own — provisioning finishes, a container starts or stops, a background probe corrects a stale Running. A sighted user sees the row redraw. A screen reader user gets nothing: VS Code does not announce a TreeItem description or icon change, and the extension does not announce it either.

This was recorded as item 26 of the DocumentDB Local UX review (PR #790) and deferred as "post-redesign".

Why now

The redesign is done, and #876 changed the mechanism in a way that makes this more relevant, not less:

• Transitional states used to swap the whole row. They now apply the tree framework's node-progress overlay (ext.state.runWithTemporaryDescription), which mutates description and iconPath in place.
• An in-place mutation is exactly the case a screen reader is least likely to surface on its own.

So the states a user most needs to hear about — "starting", "stopping", "provisioning", "refreshing", and the terminal state that follows — are now the quietest ones.

Scope to investigate

• Which transitions are worth announcing, and which would be noise. A background freshness probe firing every time the view re-renders must not announce anything.
• The right mechanism: vscode.window.showInformationMessage is wrong (too heavy), an ARIA live region is a webview concept and does not apply to the tree. Options worth checking: vscode.window.setStatusBarMessage, an accessibility-specific announcement API if one exists for tree views, or accepting that the terminal state notification is the announcement.
• Whether the same gap exists for other long-running tree operations in the extension (deleting a collection, importing documents) — if so this is a shared fix, not a Quick Start one.
• Verify with an actual screen reader (NVDA / VoiceOver) rather than by reasoning about the API.

Out of scope

Webview accessibility. The Quick Start setup panel is a separate surface with its own announcer.

References

• UX review item 26 — PR #790
• Progress overlay and the bridge — #876, src/tree/connections-view/LocalQuickStart/quickStartProgressBridge.ts

Start with src/tree/connections-view/LocalQuickStart/quickStartProgressBridge.ts and trace how progress overlays mutate the tree node, then inspect related long-running tree operations and the available VS Code announcement APIs. Determine which transitions should be announced without background-refresh noise, implement the selected mechanism, and verify the result with NVDA or VoiceOver.