docs: add full-width VibeSense README hero

[stephenleo]

Summary

• replace the small README logo with a full-width adaptive hero
• add the VibeSense title and the canonical subtitle inside the banner
• preserve the approved Modern Jade mark and light/dark palette
• keep the subtitle on one line at normal README width and provide a legible two-line mobile treatment
• package the banner so the npm README image remains available

Verification

• npm run verify
• npm run build
• xmllint --noout assets/vibesense-mark.svg assets/vibesense-banner.svg
• npm pack --dry-run --json
• visual QA at README and 320px widths in light and dark themes