refactor: simplify database schema and remove role history

[kronosapiens]

Summary

• Change primary keys from UUID to serial integers for simplicity
• Simplify reactions table column names (message_author_id → author_id, reactor_role_at_time → reactor_role)
• Remove role_history table and all related code (auditing feature not needed)
• Rewrite initial migration for a clean slate

Net change: -142 lines

Database Migration Checklist

BREAKING CHANGE: This PR rewrites the initial migration schema.
The new schema is incompatible with the previous version.

Local Development

• Drop all tables:

  psql daimyo -c "DROP TABLE IF EXISTS pgmigrations, content_drafts, content_pipeline_runs, content_stories, reactions, role_history CASCADE;"

• Re-run migrations:

  cd backend
  pnpm migrate up

Railway Deployment

• Drop all tables via Railway CLI:

  # Connect to your Railway PostgreSQL
  railway connect postgres
  
  # Then run:
  DROP TABLE IF EXISTS pgmigrations, content_drafts, content_pipeline_runs, content_stories, reactions, role_history CASCADE;

  Or via psql with DATABASE_URL:

  psql "$DATABASE_URL" -c "DROP TABLE IF EXISTS pgmigrations, content_drafts, content_pipeline_runs, content_stories, reactions, role_history CASCADE;"

  Or via Railway Dashboard:

  1. Go to your Railway project → PostgreSQL service
  2. Click "Data" tab → "Query"
  3. Run the DROP TABLE command

• Trigger a redeploy (migrations run automatically on startup)

Verify Schema

# Check reactions table structure
psql <connection> -c "\d reactions"
# Should show: id (serial), message_id, author_id, reactor_id, reactor_role, timestamp

# Verify role_history is gone
psql <connection> -c "\dt"
# Should NOT include role_history

Test plan

• Build passes (pnpm build)
• All 67 tests pass (pnpm test)

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