Fix migration require paths after reorganization

- Updated all core migrations to use ../../src/ instead of ../src/
- Updated legacy migrations with the same path fix
- This fixes MODULE_NOT_FOUND errors during deployment

The error occurred because migrations were moved one level deeper
into core/ and legacy/ subdirectories without updating the relative
paths to the source files.

backend/migrations/legacy/004_add_categories_and_cms.js

@@ -1,4 +1,4 @@
-const { db } = require('../src/database/db');
+const { db } = require('../../src/database/db');
 
 async function up() {
   console.log('Adding photo categories and CMS tables...');

backend/migrations/legacy/014_add_host_name_to_events_duplicate.js

@@ -1,4 +1,4 @@
-const { db } = require('../src/database/db');
+const { db } = require('../../src/database/db');
 
 async function up() {
   // Check if host_name column already exists