Add delegate_party_id column to track which party is acting as delegate
(generates and returns user share instead of storing it).
Changes:
- Add delegate_party_id VARCHAR(255) column with default empty string
- Add partial index for faster lookups when delegate party is present
- Include up and down migrations
This fixes the issue where delegate party selection worked but the delegate_party
field was not being returned in API responses due to missing database column.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
