fix: correct Formidable API usage and move activation hooks to top level

- Replace non-existent FrmFormActionsController::create_action() with proper API
  - Use get_form_actions('wppost')->prepare_new() pattern
  - Affects job submission, edit, and deactivation forms
- Move register_activation_hook() to main plugin file top level
  - WordPress requires activation hooks at bootstrap, not in plugins_loaded
  - Fixes missing page creation on plugin activation

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

ddhh-job-manager.php

@@ -47,6 +47,10 @@ require_once DDHH_JM_PLUGIN_DIR . 'includes/class-user-preferences.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-scheduler.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-ddhh-job-manager.php';
 
+// Register activation and deactivation hooks (must be at top level).
+register_activation_hook( __FILE__, array( 'DDHH_JM_Activator', 'activate' ) );
+register_deactivation_hook( __FILE__, array( 'DDHH_JM_Deactivator', 'deactivate' ) );
+
 /**
  * Initialize the plugin.
  */