fix: correct field name in PluginManager constructor

- Change plugins to _plugins to match the struct field name

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: haasonsaas

src/plugins/plugin.rs

@@ -25,7 +25,7 @@ pub struct PluginManager {
 impl PluginManager {
     pub fn new() -> Self {
         Self {
-            plugins: HashMap::new(),
+            _plugins: HashMap::new(),
             pre_analyzers: Vec::new(),
             post_processors: Vec::new(),
         }