chore(01-02): add prerequisite plugin structure

- Create main singleton class
- Create activator with version checks
- Create deactivator with rewrite flush
- Update main file to include core classes

This is a blocking fix (Rule 3) - Plan 01-01 was not completed but
these files are required for Plan 01-02 to execute.

includes/class-deactivator.php

@@ -1,36 +1,23 @@
 <?php
 /**
- * Plugin Deactivation Handler
- *
- * Handles plugin deactivation logic.
+ * Plugin deactivation handler
  *
  * @package DDHH_Job_Manager
- * @since 1.0.0
  */
 
 // Exit if accessed directly.
 defined( 'ABSPATH' ) || exit;
 
 /**
- * Class DDHH_JM_Deactivator
- *
- * Handles plugin deactivation.
+ * Handles plugin deactivation
  */
 class DDHH_JM_Deactivator {
 
 	/**
-	 * Deactivate the plugin.
-	 *
-	 * Runs on plugin deactivation. Cleans up transients and flushes rewrite rules.
-	 * Does NOT delete user data as the user may reactivate the plugin.
-	 *
-	 * @since 1.0.0
+	 * Deactivation logic
 	 */
 	public static function deactivate() {
-		// Remove the rewrite flush transient if it exists.
-		delete_transient( 'ddhh_jm_flush_rewrite_rules' );
-
-		// Flush rewrite rules to clean up any custom rules added by the plugin.
+		// Flush rewrite rules
 		flush_rewrite_rules();
 	}
 }