Implement multiple phone numbers per workflow feature

Database Changes:
- Added twp_workflow_phones junction table for many-to-many relationship
- Updated activator to create and manage new table
- Maintained backward compatibility with existing phone_number field

Workflow Management:
- Added set_workflow_phone_numbers() and get_workflow_phone_numbers() methods
- Updated get_workflow_by_phone_number() to check both old and new structures
- Enhanced save/update handlers to support phone_numbers array
- Added AJAX endpoint for retrieving workflow phone numbers

User Interface:
- Replaced single phone number select with dynamic multi-select interface
- Added "Add Number" and "Remove" buttons for managing multiple numbers
- Updated workflow listing to display all assigned phone numbers
- Enhanced JavaScript for phone number management and validation

The webhook routing already supports multiple numbers since get_workflow_by_phone_number()
was updated to check both structures. This feature allows users to assign multiple
Twilio phone numbers to trigger the same workflow.

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

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

includes/class-twp-workflow.php

@@ -1084,15 +1084,31 @@ class TWP_Workflow {
     
     /**
      * Get workflow by phone number
+     * Now checks both the legacy phone_number field and the new junction table
      */
     public static function get_workflow_by_phone_number($phone_number) {
         global $wpdb;
-        $table_name = $wpdb->prefix . 'twp_workflows';
+        $workflows_table = $wpdb->prefix . 'twp_workflows';
+        $phones_table = $wpdb->prefix . 'twp_workflow_phones';
         
-        return $wpdb->get_row($wpdb->prepare(
-            "SELECT * FROM $table_name WHERE phone_number = %s AND is_active = 1 ORDER BY created_at DESC LIMIT 1",
+        // First check the new junction table
+        $workflow = $wpdb->get_row($wpdb->prepare(
+            "SELECT w.* FROM $workflows_table w
+             INNER JOIN $phones_table p ON w.id = p.workflow_id
+             WHERE p.phone_number = %s AND w.is_active = 1
+             ORDER BY w.created_at DESC LIMIT 1",
             $phone_number
         ));
+        
+        // If not found, fall back to legacy phone_number field
+        if (!$workflow) {
+            $workflow = $wpdb->get_row($wpdb->prepare(
+                "SELECT * FROM $workflows_table WHERE phone_number = %s AND is_active = 1 ORDER BY created_at DESC LIMIT 1",
+                $phone_number
+            ));
+        }
+        
+        return $workflow;
     }
     
     /**
@@ -1145,11 +1161,71 @@ class TWP_Workflow {
     public static function delete_workflow($workflow_id) {
         global $wpdb;
         $table_name = $wpdb->prefix . 'twp_workflows';
+        $phones_table = $wpdb->prefix . 'twp_workflow_phones';
         
+        // Delete phone numbers first
+        $wpdb->delete($phones_table, array('workflow_id' => $workflow_id), array('%d'));
+        
+        // Then delete workflow
         return $wpdb->delete(
             $table_name,
             array('id' => $workflow_id),
             array('%d')
         );
     }
+    
+    /**
+     * Set phone numbers for a workflow
+     */
+    public static function set_workflow_phone_numbers($workflow_id, $phone_numbers) {
+        global $wpdb;
+        $phones_table = $wpdb->prefix . 'twp_workflow_phones';
+        
+        // Remove existing phone numbers for this workflow
+        $wpdb->delete($phones_table, array('workflow_id' => $workflow_id));
+        
+        // Add new phone numbers
+        foreach ($phone_numbers as $phone_number) {
+            if (!empty($phone_number)) {
+                $wpdb->insert(
+                    $phones_table,
+                    array(
+                        'workflow_id' => $workflow_id,
+                        'phone_number' => $phone_number
+                    )
+                );
+            }
+        }
+        
+        return true;
+    }
+    
+    /**
+     * Get phone numbers for a workflow
+     */
+    public static function get_workflow_phone_numbers($workflow_id) {
+        global $wpdb;
+        $phones_table = $wpdb->prefix . 'twp_workflow_phones';
+        
+        $numbers = $wpdb->get_col($wpdb->prepare(
+            "SELECT phone_number FROM $phones_table WHERE workflow_id = %d",
+            $workflow_id
+        ));
+        
+        // If no numbers in junction table, check legacy field
+        if (empty($numbers)) {
+            $workflows_table = $wpdb->prefix . 'twp_workflows';
+            $legacy_number = $wpdb->get_var($wpdb->prepare(
+                "SELECT phone_number FROM $workflows_table WHERE id = %d",
+                $workflow_id
+            ));
+            if ($legacy_number) {
+                $numbers = array($legacy_number);
+                // Optionally migrate to new structure
+                self::set_workflow_phone_numbers($workflow_id, $numbers);
+            }
+        }
+        
+        return $numbers;
+    }
 }