refactor(inc, image-optimizer): restructure /inc architecture and standardize image optimizer module

- reorganized /inc directory structure for improved separation of concerns
  - grouped files into customizer, utilities, and tools
  - improved naming consistency across files (e.g. *-settings, template-tags, etc.)
  - simplified functions.php includes for better readability and maintainability

- refactored Customizer structure
  - extracted image optimizer settings from core-settings into dedicated module
  - consolidated settings, UI logic, and styles into a single feature file
  - improved naming consistency for hooks and functions

- standardized Image Optimizer admin tool
  - renamed "Performance Tools" to "Image Optimizer" across UI and hooks
  - updated admin page registration, callback names, and menu labels
  - aligned AJAX nonce naming for consistency and clarity

- preserved all existing logic and behavior (no functional changes)
- improved overall code organization and long-term maintainability

no breaking changes

inc/customizer/core-settings.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * Theme Customizer Core
+ *
+ * @package zeitfresser
+ */
+
+function zeitfresser_customize_register( $wp_customize ) {
+
+	// Live Preview support
+	$wp_customize->get_setting( 'blogname' )->transport         = 'postMessage';
+	$wp_customize->get_setting( 'blogdescription' )->transport  = 'postMessage';
+	$wp_customize->get_setting( 'header_textcolor' )->transport = 'postMessage';
+
+	if ( isset( $wp_customize->selective_refresh ) ) {
+		$wp_customize->selective_refresh->add_partial(
+			'blogname',
+			array(
+				'selector'        => '.site-title a',
+				'render_callback' => 'zeitfresser_customize_partial_blogname',
+			)
+		);
+
+		$wp_customize->selective_refresh->add_partial(
+			'blogdescription',
+			array(
+				'selector'        => '.site-description',
+				'render_callback' => 'zeitfresser_customize_partial_blogdescription',
+			)
+		);
+	}
+}
+add_action( 'customize_register', 'zeitfresser_customize_register' );
+
+/**
+ * Partial refresh helpers
+ */
+function zeitfresser_customize_partial_blogname() {
+	bloginfo( 'name' );
+}
+
+function zeitfresser_customize_partial_blogdescription() {
+	bloginfo( 'description' );
+}
+
+/**
+ * Live preview JS
+ */
+function zeitfresser_customize_preview_js() {
+	wp_enqueue_script(
+		'zeitfresser-customizer',
+		get_template_directory_uri() . '/js/customizer.js',
+		array( 'customize-preview' ),
+		ZEITFRESSER_VERSION,
+		true
+	);
+}
+add_action( 'customize_preview_init', 'zeitfresser_customize_preview_js' );