feat(frontend): refresh landing and scan experience

[KazanderDad]

Summary

• redesign the landing page for guests with new messaging and CTA buttons
• add an authenticated app header plus shared footer with developer shortcuts
• split the scan flow into dedicated My QR and Camera views and update styling across the app

Testing

• pnpm --filter frontend run lint
• pnpm --filter frontend run test
• pnpm --filter frontend run build

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Codex Task

[Copilot]

Pull Request Overview

This PR implements a comprehensive UI redesign for the Peer Mapper application, transforming it from a basic list-style interface into a polished, modern design with a cohesive dark theme and improved user experience.

• Introduces new AppHeader and AppFooter components with navigation and branding
• Refactors the home page to conditionally render marketing content for unauthenticated users and quick actions for authenticated users
• Splits the monolithic /scan page into separate /scan/my-qr and /scan/camera routes for better UX

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
frontend/src/components/AppHeader.tsx	New header with navigation, user profile display, and avatar initials generation
frontend/src/components/AppFooter.tsx	New footer with developer shortcuts and branding
frontend/src/app/page.tsx	Refactored to show marketing content when unauthenticated, quick actions when signed in
frontend/src/app/layout.tsx	Updated to use new header/footer and removed old UserSessionSummary
frontend/src/app/globals.css	Updated CSS variables for dark theme design system
frontend/src/app/(routes)/scan/page.tsx	Simplified to redirect to /scan/my-qr
frontend/src/app/(routes)/scan/my-qr/page.tsx	New page for displaying user's QR code
frontend/src/app/(routes)/scan/camera/page.tsx	Moved scan/verify logic from old /scan page
frontend/package.json	Updated lint command to use ESLint directly
frontend/eslint.config.mjs	Added rule overrides for React hooks
frontend/tests/scan-camera-page.test.tsx	Updated test to reference new page location and wrap store resets in act
frontend/tests/navigation.test.tsx	Removed obsolete test for old home page link structure
frontend/tests/home-page.test.tsx	New tests for updated home page conditional rendering
frontend/tests/app-header.test.tsx	New tests for header component

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