[dx] Add favicon, Open Graph metadata, and page titles to all routes

[MarvyNwaokobia]

What needs to be done

The app currently has no favicon and generic page titles.
Add proper metadata to make the app look professional when shared.

Changes needed

app/layout.tsx — add to metadata export:

export const metadata: Metadata = {
  title: {
    template: '%s | Shielded Protocol',
    default: 'Shielded Protocol — Private DeFi on Stellar',
  },
  description: 'Shield your DeFi positions from public view. Compliant ZK privacy on Stellar Soroban.',
  openGraph: {
    title: 'Shielded Protocol',
    description: 'Private, compliant DeFi on Stellar.',
    url: 'https://shielded.xyz',
    siteName: 'Shielded Protocol',
    type: 'website',
  },
  twitter: {
    card: 'summary_large_image',
    title: 'Shielded Protocol',
    description: 'Private, compliant DeFi on Stellar.',
  },
};

Individual route metadata:

• app/portfolio/page.tsx → title: 'Portfolio'
• app/deposit/page.tsx → title: 'Deposit'
• app/withdraw/page.tsx → title: 'Withdraw'
• app/compliance/page.tsx → title: 'Compliance'

public/ directory:

• Add favicon.ico (any simple shield icon — can use https://favicon.io)
• Add og-image.png (1200x630, simple branded image)

Definition of done

• All pages have unique <title> values
• Open Graph tags present in page source
• Favicon shows in browser tab
• pnpm build passes with no errors

Estimated time

1 hr

Required knowledge

Next.js metadata API. No crypto knowledge needed.