auto-claude: subtask-1-1 - Create Supabase middleware client utility

Created middleware.ts with Supabase client configured for Next.js middleware context.
Uses NextRequest/NextResponse cookie handling instead of next/headers.

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

src/lib/supabase/middleware.ts

@@ -0,0 +1,37 @@
+import { createServerClient } from '@supabase/ssr';
+import { NextRequest, NextResponse } from 'next/server';
+
+export async function createClient(request: NextRequest) {
+  let response = NextResponse.next({
+    request: {
+      headers: request.headers,
+    },
+  });
+
+  const supabase = createServerClient(
+    process.env.NEXT_PUBLIC_SUPABASE_URL!,
+    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
+    {
+      cookies: {
+        getAll() {
+          return request.cookies.getAll();
+        },
+        setAll(cookiesToSet) {
+          cookiesToSet.forEach(({ name, value, options }) =>
+            request.cookies.set(name, value)
+          );
+          response = NextResponse.next({
+            request: {
+              headers: request.headers,
+            },
+          });
+          cookiesToSet.forEach(({ name, value, options }) =>
+            response.cookies.set(name, value, options)
+          );
+        },
+      },
+    }
+  );
+
+  return { supabase, response };
+}