FCR-1: Set ignoreBuildErrors to false in next.config.mjs
FCR-2: Default API_URL to production backend so static builds work correctly;
.env.local overrides to localhost for local dev
FCR-3: Remove createConversation call in handleSend; generate UUID client-side
and let backend streamChat auto-create the conversation to avoid duplicate writes
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>