Add WebP conversion and garbage collection to MLS plugin

Image handling improvements:
- Convert PNG and images >500KB to WebP format
- Resize images wider than 1600px maintaining aspect ratio
- Check for .webp version before falling back to original
- WebP quality set to 80 (equivalent to JPEG 90%)

Garbage collection for disk space management:
- New MLS_Garbage_Collector class runs after each sync
- Only active when MLS_GC_DISK_THRESHOLD defined in wp-config
- Deletes image directories older than 24 hours, oldest first
- Stops when free space reaches 5GB or 2GB deleted per run
- Protects recently accessed images from deletion

Documentation:
- Added Garbage Collection section to README
- Updated Features list and File Structure

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

wp-content/plugins/mls-by-hansonxyz/cli/class-mls-cli.php

@@ -512,6 +512,45 @@ class MLS_CLI {
         if (!$result['success']) {
             WP_CLI::halt(1);
         }
+
+        // Run garbage collection after successful sync
+        if ($result['success']) {
+            $gc = $this->plugin->get_garbage_collector();
+            if ($gc && $gc->is_enabled()) {
+                if (!$silent) {
+                    WP_CLI::line('');
+                    WP_CLI::line('=== MLS Image Garbage Collection ===');
+                    WP_CLI::line('');
+                }
+
+                $gc_result = $gc->run($status_callback);
+
+                if (!$silent && $gc_result['ran']) {
+                    WP_CLI::line(sprintf(
+                        'Deleted: %d directories (%s)',
+                        $gc_result['deleted_count'],
+                        $this->format_bytes($gc_result['deleted_bytes'])
+                    ));
+                }
+            }
+        }
+    }
+
+    /**
+     * Format bytes to human readable string
+     *
+     * @param int $bytes Bytes
+     * @return string Formatted string
+     */
+    private function format_bytes($bytes) {
+        if ($bytes >= 1073741824) {
+            return number_format($bytes / 1073741824, 2) . ' GB';
+        } elseif ($bytes >= 1048576) {
+            return number_format($bytes / 1048576, 2) . ' MB';
+        } elseif ($bytes >= 1024) {
+            return number_format($bytes / 1024, 2) . ' KB';
+        }
+        return $bytes . ' bytes';
     }
 
     /**