fix(middleware): remove explicit runtime export

Middleware automatically runs on Edge runtime in Next.js 15+.
The explicit runtime='edge' export caused build error:
'the edge runtime for rendering is currently experimental'

Fix: Remove runtime export - middleware is Edge by default.

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

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

Author: apex-ai-net

middleware.ts

@@ -4,8 +4,8 @@ import { addSecurityHeaders } from './lib/security-headers'
 import { validateCsrf } from './lib/csrf-edge'
 import { logger } from './lib/logger'
 
-// Explicitly specify Edge runtime for Netlify Edge Functions
-export const runtime = 'edge'
+// Note: Middleware automatically runs on Edge runtime in Next.js 15+
+// No need to declare export const runtime = 'edge'
 
 const isProtectedRoute = createRouteMatcher(['/dashboard(.*)', '/student-intake', '/preceptor-intake'])
 const isPublicRoute = createRouteMatcher(['/sign-in(.*)', '/sign-up(.*)', '/', '/api/webhook(.*)', '/help', '/terms', '/privacy'])