Add CSV import coverage

[tunguz]

Summary

• Add focused Vitest coverage for CSV table imports.
• Cover empty body, unsupported content types, missing multipart files, empty CSV data, raw text/csv imports, JSON-wrapped CSV column mapping, and partial insert failures.
• This raises src/import/csv.ts from 0% coverage to 93.22% statements / 85.71% branches in the coverage run.

Validation

• npx -y pnpm@10 vitest run src/import/csv.test.ts
• npx -y pnpm@10 vitest run src/import/csv.test.ts src/import/json.test.ts src/import/dump.test.ts
• npx -y pnpm@10 vitest run --coverage.enabled true --coverage.reportOnFailure --coverage.reportsDirectory ./coverage (current main still exits nonzero because four src/rls/index.test.ts expectations fail and global branch coverage remains below 75%; the new CSV import tests pass and overall line coverage reports 80.38%.)

Demo Video

• Short demo video (raw mp4)

/claim #71