Drop tsx watch mode — use plain tsx for dev server

tsx watch hangs when puppeteer/chromium imports are involved.
Plain tsx starts reliably. Hot reload isn't critical since
server changes are infrequent compared to client changes.

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

package.json

@@ -4,7 +4,7 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev:server": "tsx watch --clear-screen=false src/server/index.ts",
+    "dev:server": "tsx src/server/index.ts",
     "dev:client": "cd src/client && npm run dev",
     "dev": "concurrently --names server,client \"npm run dev:server\" \"npm run dev:client\"",
     "build:client": "cd src/client && npm run build",