fix(types): replace any with proper type in better-auth auth

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

convex/betterAuth/auth.ts

@@ -1,3 +1,3 @@
 import { createAuth } from '../auth';
 
-export const auth = createAuth({} as any);
+export const auth = createAuth({} as Parameters<typeof createAuth>[0]);