feat: re-enable migration 004 for active identity phase c

- Uncomment migration 004_drop_settings_activeDid_column
- Phase 1 component migration complete, safe to drop legacy column
- Migration system now runs all 4 migrations successfully

This completes the legacy activeDid column removal after
12 critical identity components were migrated to use the
new Active Identity façade.

src/db-sql/migration.ts

@@ -180,6 +180,7 @@ const MIGRATIONS = [
       END;
     `,
   },
+  // Migration 004 re-enabled - Phase 1 complete, critical components migrated
   {
     name: "004_drop_settings_activeDid_column",
     sql: `