Add dashboard preview to README

[lrqnet]

Summary

• add a real dark-mode desktop dashboard preview to the public README
• keep the capture reproducible with an explicit, password-gated fictional-data seeder
• verify that the preview contains only reserved documentation addresses and no metadata or sensitive data

Validation

• Pint, PHPStan and PHPUnit: 214 passed, 5 skipped
• Prettier, ESLint, TypeScript, translation parity and production build
• isolated Docker capture stack, visual review, asset metadata review and git diff --check

No runtime image, tag, or release is required: this PR only adds public documentation and its reproduction fixture.