refactor: Use plugin registry for filter service discovery

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/filter_plugin/head.rs

@@ -1,6 +1,7 @@
 use super::{FilterPlugin, FilterOption};
 use std::io::{Result, Read, Write, BufRead};
 use crate::common::PIPESIZE;
+use crate::services::filter_service::register_filter_plugin;
 
 pub struct HeadBytesFilter {
     remaining: usize,
@@ -96,3 +97,10 @@ impl FilterPlugin for HeadLinesFilter {
         ]
     }
 }
+
+// Register the plugin at module initialization time
+#[ctor::ctor]
+fn register_head_filters() {
+    register_filter_plugin("head_bytes", || Box::new(HeadBytesFilter::new(0)));
+    register_filter_plugin("head_lines", || Box::new(HeadLinesFilter::new(0)));
+}