docs: add Clerk setup guide and improve auth error messages

- Create CLERK_SETUP.md with step-by-step instructions
- Improve error message to indicate Clerk configuration issue
- Remove debug logging from auth middleware
- Update error handling to be more helpful

The 401 error is caused by missing Clerk Secret Key in server/.env

src/services/reportService.ts

@@ -50,7 +50,7 @@ class ReportService {
 
     if (!response.ok) {
       if (response.status === 401) {
-        throw new Error('You must be signed in to upload photos. Please sign in and try again.');
+        throw new Error('Authentication failed. Please make sure the backend Clerk Secret Key is configured correctly.');
       }
       
       // Try to get error details from response