docs: redesign README with badges and VHS-recorded demos

[Etoile-Bleu]

Summary

• Applies the same visual treatment ZamSync's README already uses: a badge row (CI, release, license, platforms, dev.to article link), a hero GIF right under the disclaimer, and a features table. Sections that don't apply to MenSung (Docker, PKI, Prometheus, sponsors) were left out rather than copied blindly.
• Three real terminal recordings (vhs + ttyd + headless Chrome, not mockups) of the actual mensung binary: a CLI interaction check, a second CLI check, and the TUI's Alt+I drug info screen with scrolling. .tape sources committed alongside the GIFs in docs/demos/ so they're reproducible.
• Fixes a real accuracy bug found while recording these: the enriched dataset's exact INN name is "Acetylsalicylic acid", not "Aspirin", so the README's old example would return "Unknown drug" against the database mensung installs by default today.

Test plan

• Verified mensung 'Acetylsalicylic acid' Warfarin and mensung Warfarin Ibuprofen both resolve and match the GIFs against the current enriched database
• grep -c "—" returns 0 (no em dashes, per GOOD_PRACTICE.md)
• All internal doc links (#security-model, #usage, etc.) unchanged from the existing README