Reorganize migrations for new vs existing deployments

- Created core/ directory for essential migrations that always run
- Created legacy/ directory for migrations only needed when upgrading
- New deployments will only run core migrations for a clean database
- Existing deployments will run all migrations in proper sequence
- Fixed duplicate migration numbers (014 and 027)
- Updated migration runners to handle new directory structure
- Added README explaining the migration organization

This change optimizes deployment for new users who will get a clean
schema without running unnecessary upgrade migrations.

backend/migrations/legacy/024_fix_boolean_compatibility.js

@@ -0,0 +1,29 @@
+/**
+ * Fix boolean compatibility issues between PostgreSQL and SQLite
+ * This migration updates the database configuration and existing data
+ */
+
+exports.up = async function(knex) {
+  const isPostgres = knex.client.config.client === 'pg';
+  
+  if (!isPostgres) {
+    // Enable foreign keys for SQLite
+    await knex.raw('PRAGMA foreign_keys = ON');
+    
+    // Note: SQLite stores booleans as 0/1
+    // No data migration needed as Knex handles this automatically
+    // But queries must use formatBoolean() helper
+    
+    console.log('SQLite boolean compatibility check:');
+    console.log('- SQLite stores booleans as 0/1');
+    console.log('- All boolean comparisons should use formatBoolean() helper');
+    console.log('- Foreign keys enabled');
+  }
+  
+  return Promise.resolve();
+};
+
+exports.down = async function(knex) {
+  // No rollback needed
+  return Promise.resolve();
+};