feat(0.6.2): current version badge on Settings page

Small grey pill follows the "Radio — Settings" H1 — v{RADIO_VERSION}.
Visible at a glance so you don't have to hover the plugin row in
Plugins → Installed or open About just to check what version you're on.
Dark-theme variant so it stays readable when theme=dark.

Files: radio.php (version), inc/settings.php (<span> inside H1),
assets/css/radio.css (.radio-version-badge + dark override),
inc/about.php (rotate v0.6.2 into latest expanded slot, v0.6.1 into
earlier-releases list), CHANGELOG.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

inc/settings.php

@@ -47,7 +47,10 @@ function radio_render_settings_page() {
     $hide_widget = ! empty( $state['hide_dashboard_widget'] );
     ?>
     <div class="wrap radio-settings-wrap">
-        <h1><?php esc_html_e( 'Radio — Settings', 'radio' ); ?></h1>
+        <h1>
+            <?php esc_html_e( 'Radio — Settings', 'radio' ); ?>
+            <span class="radio-version-badge">v<?php echo esc_html( RADIO_VERSION ); ?></span>
+        </h1>
 
         <form method="post" action="">
             <?php wp_nonce_field( 'radio_save_settings', 'radio_settings_nonce' ); ?>