Fix frontend build and stabilize test suite

[vsxd]

Summary

• fix the frontend build break and add the missing GET mapping for skill search
• align backend tests with current auth/session, token, slug resolution, and audit log behavior
• make the test profile usable on H2 by adjusting test-only auth/schema behavior

Verification

•  ERR_PNPM_NO_IMPORTER_MANIFEST_FOUND  No package.json (or package.yaml, or package.json5) was found in "/Users/xudongsun/github/skillhub".
•  ERR_PNPM_NO_IMPORTER_MANIFEST_FOUND  No package.json (or package.yaml, or package.json5) was found in "/Users/xudongsun/github/skillhub".