Lazy-load puppeteer to fix tsx watch hanging on startup

Puppeteer import at top level was blocking tsx watch mode,
preventing the server from starting. Now imported dynamically
only when a JS-rendered store is actually scraped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -4,9 +4,9 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev:server": "tsx watch src/server/index.ts",
+    "dev:server": "tsx watch --clear-screen=false src/server/index.ts",
     "dev:client": "cd src/client && npm run dev",
-    "dev": "concurrently \"npm run dev:server\" \"npm run dev:client\"",
+    "dev": "concurrently --names server,client \"npm run dev:server\" \"npm run dev:client\"",
     "build:client": "cd src/client && npm run build",
     "build:server": "tsc",
     "build": "npm run build:client && npm run build:server",