Import existing applications from CSV/JSON

[Joun-Mikhail]

Summary

Complement the new CSV export with an import flow so users can migrate from a spreadsheet.

Proposed approach

• POST /api/v1/applications/import accepting CSV or JSON, with row-level validation and a dry-run mode that returns a diff.
• Frontend: drag-and-drop on the Applications page; show a preview before committing.

Acceptance criteria

• Validates and reports per-row errors without aborting the whole import.
• Maps company names to existing companies or creates them.
• Covered by integration tests (valid, partially-invalid, duplicate rows).