refactor: consolidate HTTP client for TCP/Unix socket handling

Extract reqwest client creation into dedicated HttpClient abstraction that handles both TCP and Unix socket connections transparently. Simplifies proxy logic by removing duplicate URL construction and client selection throughout the codebase.

src/handlers/assets.rs

@@ -60,17 +60,10 @@ pub async fn proxy_icons_handler(
     let full_path = format!("/api/icons/{}", path);
     let query = req.uri().query().unwrap_or("");
 
-    let bun_url = if state.downstream_url.starts_with('/') || state.downstream_url.starts_with("./")
-    {
-        if query.is_empty() {
-            format!("http://localhost{}", full_path)
-        } else {
-            format!("http://localhost{}?{}", full_path, query)
-        }
-    } else if query.is_empty() {
-        format!("{}{}", state.downstream_url, full_path)
+    let path_with_query = if query.is_empty() {
+        full_path.clone()
     } else {
-        format!("{}{}?{}", state.downstream_url, full_path, query)
+        format!("{full_path}?{query}")
     };
 
     // Build trusted headers with session info
@@ -86,7 +79,7 @@ pub async fn proxy_icons_handler(
         }
     }
 
-    match proxy::proxy_to_bun(&bun_url, state, forward_headers).await {
+    match proxy::proxy_to_bun(&path_with_query, state, forward_headers).await {
         Ok((status, headers, body)) => (status, headers, body).into_response(),
         Err(err) => {
             tracing::error!(error = %err, path = %full_path, "Failed to proxy icon request");