fix: production JSON parsing errors and trust proxy issue

- Set Express to trust proxy headers for proper IP detection with Traefik
- Add safe JSON parsing for email template variables and activity log metadata
- Create migration to fix invalid JSON data in database
- Add error handling to prevent JSON.parse crashes

This fixes the 500 errors caused by invalid JSON data and the trust proxy
warning from express-rate-limit when running behind Traefik.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/migrations/022_fix_json_columns.js

@@ -0,0 +1,68 @@
+exports.up = async function(knex) {
+  console.log('Fixing JSON columns in database...');
+  
+  // Fix email_templates variables column
+  const templates = await knex('email_templates').select('id', 'template_key', 'variables');
+  
+  for (const template of templates) {
+    if (template.variables && typeof template.variables === 'string') {
+      try {
+        // Check if it's already valid JSON
+        JSON.parse(template.variables);
+      } catch (e) {
+        console.log(`Fixing invalid JSON in email template ${template.template_key}`);
+        // Attempt to fix common issues
+        let fixed = template.variables;
+        
+        // If it looks like an array but isn't valid JSON, try to fix it
+        if (fixed.startsWith('[') && fixed.endsWith(']')) {
+          // Extract the content and properly format it
+          const content = fixed.slice(1, -1);
+          const items = content.split(',').map(item => item.trim().replace(/['"]/g, ''));
+          fixed = JSON.stringify(items);
+        } else {
+          // Default to empty array if we can't fix it
+          fixed = JSON.stringify([]);
+        }
+        
+        await knex('email_templates')
+          .where('id', template.id)
+          .update({ variables: fixed });
+      }
+    } else if (!template.variables) {
+      // Set default empty array for null values
+      await knex('email_templates')
+        .where('id', template.id)
+        .update({ variables: JSON.stringify([]) });
+    }
+  }
+  
+  // Fix activity_logs metadata column
+  const activities = await knex('activity_logs').select('id', 'metadata');
+  
+  for (const activity of activities) {
+    if (activity.metadata && typeof activity.metadata === 'string') {
+      try {
+        // Check if it's already valid JSON
+        JSON.parse(activity.metadata);
+      } catch (e) {
+        console.log(`Fixing invalid JSON in activity log ${activity.id}`);
+        // Default to empty object if we can't parse it
+        await knex('activity_logs')
+          .where('id', activity.id)
+          .update({ metadata: JSON.stringify({}) });
+      }
+    } else if (!activity.metadata) {
+      // Set default empty object for null values
+      await knex('activity_logs')
+        .where('id', activity.id)
+        .update({ metadata: JSON.stringify({}) });
+    }
+  }
+  
+  console.log('JSON columns fixed successfully');
+};
+
+exports.down = async function(knex) {
+  // No rollback needed - data fixes only
+};