feat(chat-client): add IDE deprecation notice

[araarush]

Problem

Amazon Q Developer IDE plugins need a consistent deprecation notice in the shared chat experience. The existing agentic coding NEW FEATURE card is no longer the appropriate welcome card, and clients may adopt the updated chat bundle before they ship durable dismissal storage.

Solution

• Replace the agentic coding feature card with a shared warning-style deprecation notice.
• Show the notice only in new chats, never restored conversations.
• Show it at most once per chat-client instance as a safe fallback for clients without persistence wiring.
• Accept deprecationNoticeAcknowledged during chat initialization and emit client-deprecation-notice through the existing prompt-option acknowledgement event.
• Preserve the approved message and Learn more link in the shared chat client so all IDE hosts render the same content.

Testing

• npm run compile -w chat-client
• npm run test:unit -w chat-client — 219 passing, 1 pending

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.