refactor: clean up unused binding and simplify Mutex patterns

- plugin_loader.rs: remove unused _plugin_id binding in discover_plugins
- http/mod.rs: simplify config() and player_status() Mutex access patterns

src/core/plugin_loader.rs

@@ -146,11 +146,11 @@ impl PluginLoader {
                 continue;
             }
 
-            // 跳过非插件文件（如 registry.json）
-            let _plugin_id = match path.file_name().and_then(|n| n.to_str()) {
-                Some(name) if name != "registry.json" => name.to_string(),
+            // Skip non-plugin entries (e.g. registry.json)
+            match path.file_name().and_then(|n| n.to_str()) {
+                Some(name) if name != "registry.json" => {}
                 _ => continue,
-            };
+            }
 
             // 扫描版本子目录
             for version_entry in std::fs::read_dir(&path)? {