Normalize register-anon bearer tokens

[aiirvizionz]

Summary

• normalize register-anon Bearer headers with case-insensitive scheme handling and extra whitespace trimming
• reject empty Bearer headers before creating a Supabase server client or calling auth.getUser
• add focused route tests for normalized and empty authorization headers

Tests

• vitest run src/app/api/auth/register-anon/route.test.js
• node --check src/app/api/auth/register-anon/route.js
• node --check src/app/api/auth/register-anon/route.test.js
• git diff --check