fix(frontend): set preview port to 3000 to match traefik loadbalancer

Vite preview defaults to port 4173 but traefik routes to port 3000.
Added --port 3000 to the preview script in package.json.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/frontend/package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "dev": "vite --host 0.0.0.0",
     "build": "tsc --noEmit && vite build",
-    "preview": "vite preview --host 0.0.0.0",
+    "preview": "vite preview --host 0.0.0.0 --port 3000",
     "typecheck": "tsc --noEmit",
     "lint": "biome check --diagnostic-level=error src/",
     "format": "biome format --write src/"