Fix nixpacks build: add start script and configure build phase

nixpacks.toml

@@ -1,5 +1,2 @@
 [phases.build]
-cmds = ["npm ci", "npm run build"]
+cmds = ["npm run build"]
-
-[start]
-cmd = "npx serve dist -l 3000 -s"

package.json

@@ -7,6 +7,7 @@
     "dev": "vite",
     "build": "vite build",
     "preview": "vite preview",
+    "start": "npx serve dist -l 3000 -s",
     "typecheck": "tsc --noEmit"
   },
   "devDependencies": {