feat(01-01): initialize Next.js 16 project with TypeScript and Tailwind

- Next.js 16.1.6 with App Router and src/ directory
- TypeScript configuration with path aliases (@/*)
- Tailwind CSS v4 with PostCSS setup
- ESLint with Next.js config
- Supabase packages: @supabase/supabase-js, @supabase/ssr
- Form packages: zod, react-hook-form
- Simple Leopost placeholder page

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

postcss.config.mjs

@@ -0,0 +1,7 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+
+export default config;