Ask for API keys before sending the first message

[jerelvelarde]

The chat now explains that OpenAI and Jev API keys are required before the first message. Sending text or selecting an example without keys opens the setup dialog before CopilotKit adds a message or starts an agent request.

The draft survives canceling setup and saving keys, including the chat remount. After setup, the user can send the preserved message; it is not sent automatically. New chat and Clear keys clear the draft. Updated onboarding copy and documentation explain the requirement; shared server credentials remain supported for direct API clients.

Validation:

• Regression tests cover submission gating, example prompts, cancel, saving keys across remount, and New chat.
• Browser verified the upfront notice, Enter-to-setup, preserved draft after cancel, and example-to-setup flow.
• All 159 JavaScript tests, explicit TypeScript checks, lint, and production build passed. The 111 Python tests remain unchanged from the passing parent revision.
• Independent review found no actionable issues.