Show the demo Note only on the Dashboard

[dreamerlyq-arch]

The green demo Note currently appears throughout the DAO site. Restrict the shared layout banner to the Dashboard root route (/), so all other pages omit it on both desktop and mobile. The existing demo-DAO condition, message, and links are preserved.

Validation:

• ESLint passed for the changed file; git diff --check passed.
• All 144 existing web script tests passed.
• Verified in the existing Chrome session: the Dashboard retains the Note and client navigation to Proposals removes it. Other main navigation routes also omit it from their rendered shell.
• Browser checks were limited to banner visibility; some direct navigations in the local dev server remained in the existing content-loading state. Mobile was checked through the shared layout code, not a separate viewport run.

[github-actions]

• comment: e687b1c
  preview: https://degov-7o3k9xj8o-itering.vercel.app https://degov-dev.vercel.app