[desktop] Use custom Tauri command for HTTP requests instead of http-client plugin

Replaced the http-client plugin, as it does not support keep-alive connections.
Each request opened a new TCP connection to the service, which was inefficient.

The new custom `send_tauri_http_request` command, exposed to the UI, uses an application-wide `reqwest::Client`, which supports idle (persistent) connections.

desktop/tauri/src-tauri/src/commands/mod.rs

@@ -0,0 +1 @@
+pub mod tauri_http;

desktop/tauri/src-tauri/src/commands/tauri_http.rs

@@ -0,0 +1,75 @@
+use tauri::State;
+use reqwest::{Client, Method}; 
+use serde::{Deserialize, Serialize};
+
+/// Creates and configures a shared HTTP client for application-wide use.
+/// 
+/// Returns a reqwest Client configured with:
+/// - Connection pooling
+/// - Persistent cookie store
+/// 
+/// Client can be accessed from UI through the exposed Tauri command `send_tauri_http_request(...)`
+/// Such requests execute directly from the Tauri app binary, not from the WebView process
+pub fn create_http_client() -> Client {
+    Client::builder()
+        // Maximum idle connections per host
+        .pool_max_idle_per_host(10)
+        // Enable cookie support
+        .cookie_store(true)
+        .user_agent("Portmaster UI")
+        .build()
+        .expect("failed to build HTTP client")
+}
+
+#[derive(Deserialize)]
+pub struct HttpRequestOptions {
+  method: String,
+  headers: Vec<(String, String)>,
+  body: Option<Vec<u8>>,
+}
+
+#[derive(Serialize)]
+pub struct HttpResponse {
+  status: u16,
+  status_text: String,
+  headers: Vec<(String, String)>,
+  body: Vec<u8>,
+}
+
+#[tauri::command]
+pub async fn send_tauri_http_request(
+  client: State<'_, Client>,
+  url: String,
+  opts: HttpRequestOptions
+) -> Result<HttpResponse, String> {
+  //println!("URL: {}", url);
+
+  // Build the request
+  let mut req = client
+    .request(Method::from_bytes(opts.method.as_bytes()).map_err(|e| e.to_string())?, &url);
+
+  // Apply headers
+  for (k, v) in opts.headers {
+    req = req.header(&k, &v);
+  }
+
+  // Attach body if present
+  if let Some(body) = opts.body {
+    req = req.body(body);
+  }
+
+  // Send and await the response
+  let resp = req.send().await.map_err(|e| e.to_string())?;
+
+  // Read status, headers, and body
+  let status = resp.status().as_u16();
+  let status_text = resp.status().canonical_reason().unwrap_or("").to_string();
+  let headers = resp
+    .headers()
+    .iter()
+    .map(|(k, v)| (k.to_string(), v.to_str().unwrap_or("").to_string()))
+    .collect();
+  let body = resp.bytes().await.map_err(|e| e.to_string())?.to_vec();
+
+  Ok(HttpResponse { status, status_text, headers, body })
+}