docs: embed 100% offline proof demo GIF in README

[gzz727007]

🦭 Pull Request Description

Summary of Changes

• High-Fidelity Offline Proof Demo: Added .github/assets/demo.gif (3.46 MB) showcasing real client-side execution in an authentic English browser environment.
• Hero Embed in READMEs: Updated both README.md and README.zh-CN.md to embed the demo GIF directly below the badges and live app links for maximum social proof.
• Verification Caption: Added clear bilingual captions demonstrating client-side bisection compression of a 4.14 MB real US visa sample document down to 1.8 MB entirely in browser RAM with DevTools set to Offline and Fetch/XHR verifying 0 network requests.

Type of Change

• 🐛 Bug fix (non-breaking change fixing an issue)
• ✨ New feature (non-breaking change adding functionality)
• ⚡ Performance optimization (rendering, memory, or bundle size)
• 🎨 UI / UX refinement
• 🌍 Internationalization / Translations (new or updated language)
• 📝 Documentation update (README, Guides, Comments)
• 🧪 Test suite enhancement

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🛡️ Privacy & Quality Checklist

• 100% Client-Side Invariant: All code runs strictly in the browser RAM / WebAssembly. No user documents or telemetry data are ever sent over the network.
• Automated Tests: I have verified that all existing tests pass (npm test).
• New Tests Added: I have added unit or E2E tests covering new algorithmic behavior (if applicable).
• Responsive & Cross-Browser: Verified that UI works smoothly across desktop and mobile screens.
• Self-Review: I have performed a self-review of my own code and removed unnecessary console.log statements.

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Related Issues

Closes # (Improves repository social proof and user trust prior to Product Hunt launch)

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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