Add project scaffolding and build configuration

Initialize the session-viewer project — a tool for browsing, filtering,
redacting, and exporting Claude Code session logs as self-contained HTML.

Scaffolding includes:
- package.json with Express server + React client dual-stack setup,
  dev/build/test/lint/typecheck scripts, and a CLI bin entry point
- TypeScript configs: base tsconfig.json (ESNext, bundler resolution,
  strict, react-jsx) and tsconfig.server.json extending it for the
  Express server compilation target
- Vite config: React plugin, Tailscale-aware dev server on :3847 with
  API proxy to :3848, client build output to dist/client
- Vitest config: node environment, test discovery from tests/unit and
  src/client/components
- ESLint flat config: typescript-eslint recommended, unused-vars with
  underscore exception
- Tailwind CSS config scoped to src/client, PostCSS with autoprefixer
- Playwright config: Chromium-only E2E against dev server
- bin/session-viewer.js: CLI entry point that re-execs via tsx with
  browser-open flag

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

tailwind.config.js

@@ -0,0 +1,8 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: ["./src/client/**/*.{html,tsx,ts}"],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};