fix(users): exclude current user from search

[rissrice2105-agent]

Summary

• exclude the authenticated user from search with the auth_user_id column instead of the internal profile id
• add a focused regression test for the Supabase query filter

Fixes #158

Validation

• focused Vitest route test: 1 passed (minimal Node config used because the repository's default @vitejs/plugin-react / Vite dependency mismatch aborts before test collection)
• npx oxlint src/app/api/users/search/route.js src/app/api/users/search/route.test.js (passes with the existing unused params warning)
• git diff --check