Fix zero-config demo: default profile groq_cloud + Gemini image keyless fallback

Make demo deployable on Hugging Face Spaces + add local/Groq/demo onboarding

feat: BYOK modal - visitors enter their own Groq key, stored in sessionStorage, auto-deleted on tab close

feat: add groq_cloud profile with Groq LLM + Pollinations image generation (fully free, no credits)

feat: add profiles.py control panel and Gemini backend for prompt expansion and image generation

feat: initial release of Multiverse AI Studio