feat(contact-form): implement modal contact form with AJAX submission

Replace mailto link with modal popup containing Formidable job application form. Modal stays open after submission to show success message.

Changes:
- Add modal popup with contact form on job detail pages
- Implement AJAX form submission to prevent page reload
- Auto-populate job_id field when modal opens
- Add field key compatibility for both job_id and job_id2
- Fix form ID comparison to use loose equality
- Keep modal open after submission to display success message
- Add modal styling and close functionality

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

includes/class-notifications.php

@@ -339,7 +339,7 @@ class DDHH_JM_Notifications {
 	public static function send_provider_application_notification( $entry_id, $form_id ) {
 		// Only process job application form submissions
 		$application_form_id = DDHH_JM_Formidable::get_job_application_form_id();
-		if ( $form_id !== $application_form_id ) {
+		if ( $form_id != $application_form_id ) {
 			return;
 		}
 
@@ -372,6 +372,7 @@ class DDHH_JM_Notifications {
 					$applicant_message = sanitize_textarea_field( $value );
 					break;
 				case 'job_id':
+				case 'job_id2':
 					$job_id = absint( $value );
 					break;
 			}