Remove Vue scaffolding and add design system foundation

Strip default Vue components (HelloWorld, TheWelcome, icons, AboutView),
base.css, and placeholder assets. Add Sora font (self-hosted WOFF2),
Electric Dusk color palette, and design system spec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/__tests__/HelloWorld.spec.ts

@@ -1,11 +0,0 @@
-import { describe, it, expect } from 'vitest'
-
-import { mount } from '@vue/test-utils'
-import HelloWorld from '../HelloWorld.vue'
-
-describe('HelloWorld', () => {
-  it('renders properly', () => {
-    const wrapper = mount(HelloWorld, { props: { msg: 'Hello Vitest' } })
-    expect(wrapper.text()).toContain('Hello Vitest')
-  })
-})