fix(examples/sveltekit): use node provider with bun install

Railpack doesn't have a bun provider, but we can use node provider
and override the install command to use bun.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: robelest

examples/sveltekit/railpack.json

@@ -1,4 +1,14 @@
 {
 	"$schema": "https://schema.railpack.com",
-	"provider": "bun"
+	"provider": "node",
+	"packages": {
+		"bun": "latest"
+	},
+	"steps": {
+		"install": {
+			"commands": [
+				{ "cmd": "bun install" }
+			]
+		}
+	}
 }