feat(m1): project foundation setup - Next.js 15, Tailwind, tooling, CI

- Configure Next.js 15 (App Router, Node.js runtime, serverExternalPackages for better-sqlite3/bcrypt)

- Add Tailwind CSS, PostCSS, tsconfig with @/* alias

- Create app structure (layout, page, globals.css)

- Create directory structure (lib, repositories, services, components, tests)

- Configure Vitest (alias, coverage), Playwright

- Add dependencies: next, react, better-sqlite3, bcrypt, react-markdown, etc.

- Add .env.example, CI workflow, next-env.d.ts

- Remove boilerplate src/example files

app/globals.css

@@ -0,0 +1,3 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;