feat: Add slug pattern and sortable fields to milestones collection

- slug: {{year}}-{{month}}-{{day}}-{{slug}} for date-based filenames
- sortable_fields: [filename] for sorting by filename

admin/config.yml

@@ -67,8 +67,10 @@ collections:
     folder: "docs/milestones"
     create: true
     extension: "md"
+    slug: "{{year}}-{{month}}-{{day}}-{{slug}}"
     identifier_field: "name"
     summary: "{{filename}}"
+    sortable_fields: ["filename"]
     fields:
       - {label: "Content", name: "body", widget: "markdown"}