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>

bin/session-viewer.js

@@ -0,0 +1,24 @@
+#!/usr/bin/env node
+
+// This bin script needs tsx to run TypeScript source directly.
+// Use --import to register the tsx loader before importing our TS entry.
+import { execFileSync } from "child_process";
+import { fileURLToPath } from "url";
+import path from "path";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const entryPoint = path.resolve(__dirname, "../src/server/index.ts");
+
+// Re-exec with tsx if not already running under it
+try {
+  execFileSync(
+    "npx",
+    ["tsx", entryPoint],
+    {
+      stdio: "inherit",
+      env: { ...process.env, SESSION_VIEWER_OPEN_BROWSER: "1" },
+    }
+  );
+} catch {
+  process.exit(1);
+}