refactor: define blog schema and clean up config

src/content/config.ts

@@ -1,17 +1,8 @@
-import { z, defineCollection } from "astro:content";
+import { defineCollection } from "astro:content";
+import { blogSchema } from "./schemas";
 
 const blogCollection = defineCollection({
-  schema: z.object({
+  schema: blogSchema,
-    author: z.string(),
-    datetime: z.string(), // z.string().datetime() only available in Zod v3.20.2
-    title: z.string(),
-    slug: z.string().optional(),
-    featured: z.boolean(),
-    draft: z.boolean(),
-    tags: z.array(z.string()),
-    ogImage: z.string().optional(),
-    description: z.string(),
-  }),
 });
 
 export const collections = {

src/content/schemas.ts

@@ -0,0 +1,20 @@
+import { z } from "astro:content";
+
+export const blogSchema = z.object({
+  author: z.string(),
+  publishDatetime: z.string(), // z.string().datetime() only available in Zod v3.20.2
+  title: z.string(),
+  slug: z.string().optional(),
+  featured: z.boolean(),
+  draft: z.boolean(),
+  tags: z.array(z.string()),
+  ogImage: z
+    .object({
+      src: z.string(),
+      alt: z.string().optional(),
+    })
+    .optional(),
+  description: z.string(),
+});
+
+export type BlogFrontmatter = z.infer<typeof blogSchema>;