feat: generate and normalize specs before search/export

[Gabrielgvl]

Summary

• remove query fallback inference path and resolve search/export specs via API
• call /v1/specs followed by /v1/specs/normalize before /v1/accounts/search and /v1/exports
• improve error messages when spec generation/normalization returns empty spec
• update tests to cover new flow and edge cases for register/empty-spec handling

Validation

• pnpm test
• pnpm verify