feat: rewrite to Next.js v13 app directory

Improvements:
- Hide switch theme input (ugly little white square)
- i18n without subpath (e.g: /fr or /en), same url whatever the locale used

cypress/component/Footer.cy.tsx

@@ -1,16 +0,0 @@
-import { Footer } from '@/components/Footer'
-
-describe('<Footer />', () => {
-  it('should render with appropriate link tag version', () => {
-    const version = '1.0.0'
-    cy.mount(<Footer version={version} />)
-    cy.contains('Théo LUDWIG')
-      .get('[data-cy=version-link]')
-      .should('have.text', version)
-      .should(
-        'have.attr',
-        'href',
-        `https://github.com/theoludwig/theoludwig/releases/tag/v${version}`
-      )
-  })
-})