docs: make Nova README pitch pop

[papi-ux]

Summary

• sharpen the README hero around Nova as a handheld-first client that understands the host
• move the "Why Nova" pitch above setup with a direct comparison against normal streaming clients
• add a Browse / Decide / Control visual strip using existing screenshots
• rename user-facing README copy from quick menu/Headless toward Command Center/Private Stream

Validation

• git diff --check
• bash ./scripts/check-public-docs.sh
• staged credential/private-key scan clean

Notes

• docs-only README polish after the 1.1.1 release-prep PR
• no app code or release artifact changes