feat: scaffold Next.js 16 web app with Tailwind v4

Sets up apps/web with Next.js 16, React 19, Tailwind CSS v4 (postcss plugin
config, @import syntax), Jest + Testing Library, App Router layout and home page.
2/2 tests passing, build verified.

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

apps/web/jest.config.js

@@ -0,0 +1,9 @@
+const nextJest = require('next/jest');
+
+const createJestConfig = nextJest({ dir: './' });
+
+module.exports = createJestConfig({
+  setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'],
+  testEnvironment: 'jest-environment-jsdom',
+  testMatch: ['**/*.test.tsx', '**/*.test.ts'],
+});