fix: admin branding page now shows uploaded assets — load from platform_assets table

The admin was only reading from local theme.json and platform_theme,
but uploaded emoji/asset URLs are stored in platform_assets. Now loads
them on page render so the preview thumbnails actually appear.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin/branding.php

@@ -34,6 +34,16 @@ if (is_array($themeRows) && !isset($themeRows['error'])) {
         $theme[$row['id']] = $row['value'];
     }
 }
+// Load assets from platform_assets table
+$assetRows = $sdb->get('platform_assets', ['select' => 'id,asset_url']);
+if (is_array($assetRows) && !isset($assetRows['error'])) {
+    if (!isset($theme['assets'])) $theme['assets'] = [];
+    foreach ($assetRows as $row) {
+        if ($row['asset_url']) {
+            $theme['assets'][$row['id']] = $row['asset_url'];
+        }
+    }
+}
 // Merge local file on top (for assets that are still local)
 if (file_exists($THEME_FILE)) {
     $localTheme = json_decode(file_get_contents($THEME_FILE), true) ?: [];