fix(network): explicitly disable proxy fallbacks for none and system modes

Disabled implicit system/environment variable proxy fallbacks in reqwest, yt-dlp, and aria2c when no proxy is explicitly provided. Updated useDownloadStore to strictly return 'none' when 'none' is selected or when 'system' proxy is empty, matching IDM/FDM behavior and ignoring http_proxy environment variables.

src-tauri/src/download.rs

@@ -703,7 +703,11 @@ fn build_client(payload: &DownloadPayload) -> Result<Client, String> {
         builder = builder.user_agent(user_agent);
     }
     if let Some(proxy) = payload.proxy.as_deref().filter(|value| !value.is_empty()) {
-        builder = builder.proxy(reqwest::Proxy::all(proxy).map_err(|error| error.to_string())?);
+        if proxy == "none" {
+            builder = builder.no_proxy();
+        } else {
+            builder = builder.proxy(reqwest::Proxy::all(proxy).map_err(|error| error.to_string())?);
+        }
     }
 
     builder.build().map_err(|error| error.to_string())

src-tauri/src/lib.rs

@@ -2085,8 +2085,10 @@ pub(crate) async fn start_media_download_internal(
             }
         }
 
-        if let Some(p) = proxy.as_ref() {
-            if !p.is_empty() {
+        if let Some(p) = proxy.as_ref().filter(|s| !s.is_empty()) {
+            if p == "none" {
+                cmd = cmd.arg("--proxy").arg("");
+            } else {
                 cmd = cmd.arg("--proxy").arg(p);
             }
         }

src-tauri/src/queue.rs

@@ -872,8 +872,12 @@ impl SidecarSpawner for ProductionSpawner {
         if !header_list.is_empty() {
             options.insert("header".to_string(), serde_json::json!(header_list));
         }
-        if let Some(prox) = &payload.proxy {
-            options.insert("all-proxy".to_string(), serde_json::json!(prox));
+        if let Some(prox) = payload.proxy.as_deref().filter(|s| !s.is_empty()) {
+            if prox == "none" {
+                options.insert("all-proxy".to_string(), serde_json::json!(""));
+            } else {
+                options.insert("all-proxy".to_string(), serde_json::json!(prox));
+            }
         }
         let uris = crate::collect_download_uris(&payload.url, payload.mirrors.as_deref());
         let params = serde_json::json!([uris, options]);