feat: add middleware for zine.mycofi.earth subdomain routing

Routes zine.mycofi.earth root to /zine content so it works
like zine.jeffemmett.com - showing the zine generator directly.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

middleware.ts

@@ -0,0 +1,51 @@
+import { NextResponse } from 'next/server'
+import type { NextRequest } from 'next/server'
+
+export function middleware(request: NextRequest) {
+  const host = request.headers.get('host') || ''
+  const pathname = request.nextUrl.pathname
+
+  // Handle zine.mycofi.earth subdomain
+  if (host.startsWith('zine.')) {
+    // Don't rewrite if already accessing /zine paths or API/static files
+    if (
+      pathname.startsWith('/zine') ||
+      pathname.startsWith('/api/zine') ||
+      pathname.startsWith('/_next') ||
+      pathname.startsWith('/favicon') ||
+      pathname.includes('.')
+    ) {
+      return NextResponse.next()
+    }
+
+    // Rewrite root and other paths to /zine
+    const url = request.nextUrl.clone()
+
+    if (pathname === '/') {
+      url.pathname = '/zine'
+    } else if (pathname.startsWith('/create')) {
+      url.pathname = `/zine${pathname}`
+    } else if (pathname.startsWith('/z/')) {
+      url.pathname = `/zine${pathname}`
+    } else {
+      // For any other path, try prepending /zine
+      url.pathname = `/zine${pathname}`
+    }
+
+    return NextResponse.rewrite(url)
+  }
+
+  return NextResponse.next()
+}
+
+export const config = {
+  matcher: [
+    /*
+     * Match all request paths except:
+     * - _next/static (static files)
+     * - _next/image (image optimization files)
+     * - favicon.ico (favicon file)
+     */
+    '/((?!_next/static|_next/image|favicon.ico).*)',
+  ],
+}