feat(0.6.3): discreet "buy me a coffee" support link

Tiny footer line inside the Updates panel on Settings + matching line
at the bottom of the Credits + thanks card on About. Pulled from a
single RADIO_SUPPORT_URL constant so both stay in sync. Conditional
render — if the constant is empty, the link is silently hidden, so
forks can strip funding with one line.

Design intent: muted (12px, admin-theme-coloured, subtle top divider).
Reads as housekeeping not a sales pitch — no yellow BMC brand chrome.
Dark-theme divider override so it stays subtle on the dark surface.

Files: radio.php (version, RADIO_SUPPORT_URL constant default
https://buymeacoffee.com/davidtkeane), inc/updater.php (link in
Updates panel), inc/about.php (link in Credits + thanks card; rotate
v0.6.3 → latest, v0.6.2 → earlier list), assets/css/radio.css
(.radio-support-link + dark-theme override), CHANGELOG.md.

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

inc/updater.php

@@ -195,6 +195,12 @@ function radio_render_updates_panel() {
         <p style="margin:10px 0 0; color:#646970; font-size:12px;">
             <?php esc_html_e( 'Manual update path: download the .zip, deactivate the plugin in WordPress, upload via Plugins → Add New → Upload, reactivate. Your settings survive the upgrade (state is stored in user_meta).', 'radio' ); ?>
         </p>
+
+        <?php if ( defined( 'RADIO_SUPPORT_URL' ) && RADIO_SUPPORT_URL ) : ?>
+            <a class="radio-support-link" href="<?php echo esc_url( RADIO_SUPPORT_URL ); ?>" target="_blank" rel="noopener">
+                <?php esc_html_e( 'Like Radio? If You fancy to buy me a coffee →', 'radio' ); ?>
+            </a>
+        <?php endif; ?>
     </div>
 
     <script>