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>

playwright.config.ts

@@ -0,0 +1,26 @@
+import { defineConfig, devices } from "@playwright/test";
+
+export default defineConfig({
+  testDir: "./tests/e2e",
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: "html",
+  use: {
+    baseURL: "http://localhost:3847",
+    trace: "on-first-retry",
+  },
+  projects: [
+    {
+      name: "chromium",
+      use: { ...devices["Desktop Chrome"] },
+    },
+  ],
+  webServer: {
+    command: "npm run dev",
+    url: "http://localhost:3847",
+    reuseExistingServer: !process.env.CI,
+    timeout: 30000,
+  },
+});