fix: comprehensive PostgreSQL/SQLite compatibility fixes

Critical fixes for database compatibility issues:

INSERT operations:
- Fix all INSERT queries to use .returning('id')
- Handle both PostgreSQL (returns objects) and SQLite (returns IDs)
- Fixed in: events.js, adminArchives.js, adminEvents-enhanced.js, create-test-event.js

Date operations:
- Replace SQLite-specific db.raw("datetime('now', '+30 days')")
- Use JavaScript Date objects for cross-database compatibility
- Fixed in: adminArchives.js

Database utilities:
- Add dbCompat.js utility for handling database differences
- Provides consistent API for inserts, dates, booleans, and DB-specific operations
- Centralized database compatibility logic

Migration:
- Add migration 023 documenting PostgreSQL compatibility requirements
- Ensures future developers are aware of compatibility needs

This resolves all 'not iterable' errors and ensures the application
works correctly with both PostgreSQL (production) and SQLite (development).

backend/src/utils/dbCompat.js

@@ -0,0 +1,130 @@
+/**
+ * Database Compatibility Utilities
+ * Handles differences between PostgreSQL and SQLite
+ */
+
+const { db } = require('../database/db');
+
+/**
+ * Get database client type
+ * @returns {string} 'pg' or 'sqlite3'
+ */
+function getDbClient() {
+  return process.env.DATABASE_CLIENT || 'sqlite3';
+}
+
+/**
+ * Check if using PostgreSQL
+ * @returns {boolean}
+ */
+function isPostgreSQL() {
+  return getDbClient() === 'pg';
+}
+
+/**
+ * Handle insert operations that return IDs
+ * Works with both PostgreSQL and SQLite
+ * @param {object} query - Knex query builder
+ * @returns {Promise<number>} The inserted ID
+ */
+async function insertAndGetId(query) {
+  const result = await query.returning('id');
+  
+  // PostgreSQL returns array of objects [{id: 1}]
+  // SQLite returns array of IDs [1]
+  return result[0]?.id || result[0];
+}
+
+/**
+ * Format date for database compatibility
+ * @param {Date} date - JavaScript Date object
+ * @returns {string} ISO string format that works on both databases
+ */
+function formatDateForDB(date) {
+  return date.toISOString();
+}
+
+/**
+ * Add days to a date (database agnostic)
+ * @param {Date} date - Starting date
+ * @param {number} days - Number of days to add
+ * @returns {Date} New date
+ */
+function addDays(date, days) {
+  const result = new Date(date);
+  result.setDate(result.getDate() + days);
+  return result;
+}
+
+/**
+ * Get date extraction SQL that works on both databases
+ * @param {string} column - Column name
+ * @returns {object} Knex raw query
+ */
+function dateExtractSQL(column) {
+  if (isPostgreSQL()) {
+    return db.raw(`DATE(${column})`);
+  } else {
+    // SQLite uses date() function
+    return db.raw(`date(${column})`);
+  }
+}
+
+/**
+ * Get database size query
+ * @param {string} dbName - Database name
+ * @returns {Promise<number>} Size in bytes
+ */
+async function getDatabaseSize(dbName) {
+  if (isPostgreSQL()) {
+    const result = await db.raw('SELECT pg_database_size(?) as size', [dbName]);
+    return result.rows[0]?.size || 0;
+  } else {
+    // For SQLite, check file size
+    const fs = require('fs').promises;
+    const path = require('path');
+    const dbPath = process.env.DATABASE_PATH || path.join(__dirname, '../../data/photo_sharing.db');
+    try {
+      const stats = await fs.stat(dbPath);
+      return stats.size;
+    } catch (error) {
+      console.error('Error getting SQLite database size:', error);
+      return 0;
+    }
+  }
+}
+
+/**
+ * Handle boolean values for database compatibility
+ * @param {boolean} value - Boolean value
+ * @returns {any} Database-appropriate boolean representation
+ */
+function formatBoolean(value) {
+  if (isPostgreSQL()) {
+    return value;
+  } else {
+    // SQLite stores booleans as 0/1
+    return value ? 1 : 0;
+  }
+}
+
+/**
+ * Parse boolean from database
+ * @param {any} value - Database boolean value
+ * @returns {boolean} JavaScript boolean
+ */
+function parseBoolean(value) {
+  return Boolean(value);
+}
+
+module.exports = {
+  getDbClient,
+  isPostgreSQL,
+  insertAndGetId,
+  formatDateForDB,
+  addDays,
+  dateExtractSQL,
+  getDatabaseSize,
+  formatBoolean,
+  parseBoolean
+};