README: point thumbnail to new Space-hosted brand card

Add 1200x630 brand thumbnail (3 models)

polish: add tags + model refs + thumbnail for HF discoverability

feat: ?ref=GHKN4L37 on outbound links (HF Space attribution)

feat: cleaner model labels + ?ref attribution + first-response nudge

fix(gradio6): drop theme + removed btn args

fix: drop gradio from requirements (HF provides via sdk)

fix: drop sdk_version pin, let HF select compatible gradio

fix: pin python_version 3.11 to avoid Python 3.13 audioop removal

Initial Space: Gradio chat UI for DeepSeek V3/R1 + Qwen 3.5

initial commit