docs(images): add gradio_demo.png screenshot

Generated programmatically by calling the platform's own analyze_prompt()
function on 'The capital of France is' / correct=' Paris' /
incorrect=' Rome', then rendering the 4 returned matplotlib figures
into a single 2×2 panel image with the platform's header band.

Mirrors what a user sees in the live Gradio demo at http://localhost:7860
after clicking Analyze. Includes:
  - Logit lens rank curve by layer
  - Direct logit attribution top components
  - Activation magnitude by layer
  - Narrative summary text panel

134 KB PNG at docs/images/gradio_demo.png. README image reference points
here.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: masonwyatt23