Import signers from CSV file

As a complement to batch management via Collectives, allow users to import multiple signers from a CSV file for quick bulk participant addition.

Proposed Feature

Add CSV import functionality to add multiple participants at once. This provides an alternative to Collectives for users who already have participant lists in spreadsheets or other systems.

CSV Format

account,name,email,phone,telegram,role,receive_final
jdoe,John Doe,john@example.com,+5511999999999,,signer,true
msmith,Mary Smith,mary@example.com,,,observer,false
bjones,Bob Jones,bob@example.com,+5511888888888,@bobjones,signer,true

Required Columns

• email (required)

Optional Columns

• account - Nextcloud username
• name - Participant display name
• phone - Phone number (for SMS/WhatsApp)
• telegram - Telegram username
• role - signer or observer (default: signer)
• receive_final - true or false (default: false)

UI Concept

┌─────────────────────────────────────────────────────┐
│ Add Participants                                    │
├─────────────────────────────────────────────────────┤
│                                                     │
│ [+ Individual] [+ From CSV] [+ From Collective]    │
│                                                     │
└─────────────────────────────────────────────────────┘

When clicking "From CSV":

┌─────────────────────────────────────────────────────┐
│ Import Participants from CSV                        │
├─────────────────────────────────────────────────────┤
│                                                     │
│ [📄 Choose CSV File]                                │
│                                                     │
│ Preview (first 5 rows):                             │
│ ✓ jdoe - john@example.com - Signer - Receives final│
│ ✓ msmith - mary@example.com - Observer             │
│ ✗ invalid - invalid-email - Error: Invalid email   │
│                                                     │
│ 2 valid, 1 with errors                             │
│                                                     │
│ [Download Template] [Cancel] [Import Valid Rows]   │
└─────────────────────────────────────────────────────┘

Features

• Validation: Validate emails, phone numbers, usernames, and other fields before import
• Preview: Show preview with validation status before confirming
• Error handling: Highlight invalid rows, allow importing only valid ones
• Template download: Provide CSV template for users
• Bulk configuration: Set default role and receive_final for all imported rows

Benefits

• Quick import from existing spreadsheets
• Integration with external systems (CRM, HR, etc.)
• No dependency on Collectives app
• Useful for one-time bulk imports

Related

Complements #6959 (Collectives integration) as an alternative bulk import method.

No files, tests, or entry points are identified in the issue. Start by locating the participant-addition UI and its backend handling, then trace how validation and bulk creation are tested. Done means CSV upload, preview, validation, template download, error handling, and importing valid rows work as described.