refactor: Consolidate binary detection, response building, and filter string logic

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

src/modes/server/api/common.rs

@@ -0,0 +1,37 @@
+use axum::{
+    http::{header, StatusCode},
+    response::Response,
+};
+use serde::Serialize;
+use log;
+
+pub struct ResponseBuilder;
+
+impl ResponseBuilder {
+    pub fn json<T: Serialize>(data: T) -> Result<Response, StatusCode> {
+        let json = serde_json::to_vec(&data).map_err(|e| {
+            log::warn!("Failed to serialize response: {}", e);
+            StatusCode::INTERNAL_SERVER_ERROR
+        })?;
+        
+        Response::builder()
+            .header(header::CONTENT_TYPE, "application/json")
+            .header(header::CONTENT_LENGTH, json.len().to_string())
+            .body(axum::body::Body::from(json))
+            .map_err(|e| {
+                log::warn!("Failed to build response: {}", e);
+                StatusCode::INTERNAL_SERVER_ERROR
+            })
+    }
+    
+    pub fn binary(content: &[u8], mime_type: &str) -> Result<Response, StatusCode> {
+        Response::builder()
+            .header(header::CONTENT_TYPE, mime_type)
+            .header(header::CONTENT_LENGTH, content.len().to_string())
+            .body(axum::body::Body::from(content.to_vec()))
+            .map_err(|e| {
+                log::warn!("Failed to build response: {}", e);
+                StatusCode::INTERNAL_SERVER_ERROR
+            })
+    }
+}