Add blog series support and first post

- Add optional series field to blog collection schema (name, part)
- Update blog route to collect and sort series posts, boost related
  scoring when series matches, and render a series section with styles
  and responsive tweaks
- Add "Coffee & Code #1" blog post markdown for the new series

src/content/config.ts

@@ -7,6 +7,12 @@ const blog = defineCollection({
         description: z.string(),
         pubDate: z.coerce.date(),
         tags: z.array(z.string()).default([]),
+        series: z
+            .object({
+                name: z.string(),
+                part: z.number().int().positive(),
+            })
+            .optional(),
         draft: z.boolean().optional().default(false),
     }),
 });