feat(chat-client): add IDE deprecation notice

[araarush]

Problem

Amazon Q Developer IDE plugins need a consistent end-of-support 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 end-of-support notice.
• Use the approved heading and message across all IDE hosts.
• Link explore Kiro to https://kiro.dev and provide a separate Learn more link to the AWS end-of-support announcement.
• Show the notice in every new chat until it is acknowledged; do not insert it into restored conversations.
• Preserve the notice's warning styling and dismissal behavior when server-provided chat options are added.
• When the notice is dismissed in any tab, remove it from all open tabs, omit it from future tabs in that chat-client instance, and emit client-deprecation-notice through the existing prompt-option acknowledgement event.
• Accept deprecationNoticeAcknowledged during chat initialization so IDE hosts can persist dismissal across restarts. Clients without persistence still get a safe per-instance fallback after dismissal.

Testing

• npm run compile -w chat-client
• npm run test:unit -w chat-client — 222 passing, 1 pending
• Targeted ESLint — no branch-introduced findings
• Targeted Prettier check
• git diff --check
• Manual VS Code validation using a local Flare build, including cross-tab dismissal and persisted dismissal after restart

License

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

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 98.07692% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
chat-client/src/client/chat.ts	75.00%	1 Missing ⚠️

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