Sharpen the English demo and README workflow

[MicroMilo]

What changed

• replace the Mermaid workflow with a dedicated static SVG so GitHub controls cannot obscure the final step
• record a fully English 1920×1080 demo and regenerate the 1440×810 GIF preview
• make the extension UI locale-aware and add English built-in styling prompts
• bump the extension and package version to 0.1.1

Why

The README workflow diagram was partially covered by Mermaid's right-side controls, and the launch demo mixed Chinese UI with a low-resolution recording.

Impact

Visitors now see an unobstructed workflow and a crisp English walkthrough. Non-Chinese pages also receive an English WebMeld interface while Chinese pages keep the existing Chinese experience.

Validation

• npm run check
• npm run package
• git diff --check
• verified MP4: H.264, 1920×1080, 30fps
• verified GIF: 1440×810
• rendered and visually inspected assets/demo/how-it-works.svg
• verified dist/webmeld-0.1.1.zip integrity