refactor: replace bun with pnpm

Author: steveiliop56

.github/dependabot.yml

@@ -1,6 +1,6 @@
 version: 2
 updates:
-  - package-ecosystem: "bun"
+  - package-ecosystem: "npm"
     directory: "/"
     groups:
       minor-patch:

package.json

@@ -2,6 +2,7 @@
   "name": "tinyauth-docs-astro",
   "type": "module",
   "version": "0.0.1",
+  "packageManager": "pnpm@11.1.2",
   "scripts": {
     "dev": "astro dev",
     "start": "astro preview",