fix: keep OAuth redirect_uri clean; opener closes sign-in popup

feat: self-close sign-in popup via _target_url=/login/close

feat: delegate HF OAuth to gradio.oauth.attach_oauth

fix: harden OAuth callback token exchange against 502s

fix: add response_type=code to HF authorize request

fix: OAuth state round-trip via signed URL state; HF button at sidebar top

feat: sign in with HF and bill inference to the logged-in user

feat: switch GLM-5.2 provider to fireworks-ai

chore: remove hf token from UI configuration and rely on backend environment variable

feat: use AsyncOpenAI and set X-Accel-Buffering headers for instant streaming

chore: remove other models and add requirements.txt

feat: Add GLM-5.2 terminal-style chat UI using gradio.Server