Parse key backup auth cookies without requiring spaces

[aiirvizionz]

Summary

• accept valid Cookie headers that omit the optional space after semicolons in the key-backup auth path
• add a regression test for Supabase auth cookie parsing on GET /api/auth/key-backup

Validation

• pnpm exec vitest run --config vitest.api-temp.config.js src/app/api/auth/key-backup/route.test.js (temporary no-plugin config used because the repo Vitest config fails to load @vitejs/plugin-react/Vite in this checkout)
• node --check src/app/api/auth/key-backup/route.js
• node --check src/app/api/auth/key-backup/route.test.js
• git diff --check

Note: npx prettier --check src/app/api/auth/key-backup/route.js src/app/api/auth/key-backup/route.test.js could not run because the repo Prettier config imports missing prettier-plugin-svelte.