build: bump Astro to v4.14.2 & use content layer (#355)

Bump Astro from v4.13 to v4.14.2 and use experimental
content layer api.

src/content/config.ts

@@ -1,8 +1,10 @@
 import { SITE } from "@config";
+import { glob } from "astro/loaders";
 import { defineCollection, z } from "astro:content";
 
 const blog = defineCollection({
-  type: "content",
+  type: "content_layer",
+  loader: glob({ pattern: "**/*.md", base: "./src/content/blog" }),
   schema: ({ image }) =>
     z.object({
       author: z.string().default(SITE.author),