feat: persist chat deprecation acknowledgement

[araarush]

Summary

Persist dismissal of the shared Amazon Q chat deprecation notice in Eclipse and forward the acknowledgement state to the chat client.

The banner UI and message are owned by the shared Flare chat client. This change handles the Eclipse host-side state for the shared client-deprecation-notice message:

• stores the acknowledgement in Eclipse configuration scope, with workspace preferences as a fallback;
• forwards deprecationNoticeAcknowledged when configuring the chat client; and
• records the acknowledgement when the shared notice is dismissed.

The existing pair-programming acknowledgement behavior remains unchanged.

Scope

This PR is intentionally limited to chat deprecation dismissal persistence. It does not include README or Marketplace changes, editor-wide banner changes, or a separate Eclipse implementation of the banner UI.

Validation

Automated

• Maven/Tycho package succeeded
• Checkstyle: 0 violations
• Tests: 516 passed, 0 failed, 0 errors, 0 skipped

Manual

Validated in Eclipse using Flare 1.79.924:

• the shared notice displayed before acknowledgement;
• dismissing client-deprecation-notice persisted the acknowledgement; and
• after fully stopping and relaunching the test IDE, the notice remained hidden in a new chat.

Video

Screen.Recording.2026-09-23.at.3.22.00.PM.mov