fix: check organizations.email_domain when looking up domains for prospects

[bokelley]

Summary

• Fixed prospect discovery endpoints to check both organization_domains table AND organizations.email_domain column when looking up domains
• Added case normalization (lowercase) for consistent domain matching
• Added domain_sync_issues to domain-health endpoint to identify orgs where email_domain is set but not in organization_domains
• Added POST /api/admin/domain-health/sync endpoint to fix sync issues

Problem

Domains like tryclassify.com were appearing as new prospects even though they belong to existing accounts (Classify). This happened because:

1. The account had email_domain set on the organizations table
2. But the domain wasn't in the organization_domains table (either because it was created before that table existed, or the sync failed)
3. The prospect discovery code only checked organization_domains

Solution

Updated the SQL queries in /api/admin/slack/domains and /api/admin/email/domains to check both locations:

SELECT COALESCE(LOWER(od.domain), LOWER(o.email_domain)) as domain, ...
FROM organizations o
LEFT JOIN organization_domains od ON ...
WHERE od.domain IS NOT NULL OR LOWER(o.email_domain) = ANY($1)

Also added tools to identify and fix these sync issues via the domain-health dashboard.

Test plan

• Build passes
• All 187 tests pass
• Manually tested domain-health and domain-health/sync endpoints via curl
• Code review addressed (input validation, case normalization)

🤖 Generated with Claude Code