v0.9.88 major change sqlite to postgres

backend/src/models/migrations/004_host_plan.sql

@@ -0,0 +1,6 @@
+-- Migration 004: Host plan feature flags placeholder
+--
+-- Feature flag enforcement for APP_TYPE=host is handled in db.js initDb()
+-- which runs on every startup and upserts the correct values.
+-- This migration exists as a version marker — no SQL changes needed.
+SELECT 1;