Fix build error by moving zine.md out of content/ directory

Astro treats src/content/ as a content collection directory, which
caused a build error. Moved zine.md to src/data/ and updated
references in index.astro and README.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/pages/index.astro

@@ -4,7 +4,7 @@ import { join } from 'node:path';
 import { marked } from 'marked';
 
 // Import and parse the markdown content
-const markdownPath = join(process.cwd(), 'src/content/zine.md');
+const markdownPath = join(process.cwd(), 'src/data/zine.md');
 const markdownContent = await readFile(markdownPath, 'utf-8');
 
 // Split content into sections based on ## headers