feat(observability): add centralized diagnostics logging engine and native log viewer panel

- Configure tauri-plugin-log with 10MB rotation and 3-file retention
- Add high-frequency format filter to strip [download]% progress ticks
- Hook yt-dlp, aria2c, and native reqwest runners with lifecycle log macros
- Add export_logs Tauri command for async log file export via save dialog
- Create DiagnosticsView React component with streaming monospace console
- Apply severity highlighting: ERROR=red, WARN=yellow, INFO=grey, DEBUG=dim
- Wire Diagnostics tab into sidebar navigation and ActiveView routing
- Log native download failures to log::error! in download.rs

src-tauri/src/download.rs

@@ -189,7 +189,7 @@ impl CoordinatorEventSink {
     fn emit_failed(&self, id: Uuid, error: String) {
         match self {
             Self::Tauri(app_handle) => {
-                eprintln!("download {id} failed: {error}");
+                log::error!("native download {} failed: {}", id, error);
                 let _ = app_handle.emit("download-failed", id.to_string());
             }
             Self::Headless(event_tx) => {

src-tauri/src/ipc.rs

@@ -154,6 +154,7 @@ pub enum ActiveView {
     Scheduler,
     #[serde(rename = "speedLimiter")]
     SpeedLimiter,
+    Diagnostics,
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize, TS)]

src-tauri/src/lib.rs

@@ -1301,6 +1301,29 @@ fn delete_file(app_handle: tauri::AppHandle, path: String) -> Result<(), String>
     }
 }
 
+#[tauri::command]
+async fn export_logs(app_handle: tauri::AppHandle, dest_path: String) -> Result<String, String> {
+    use tauri::Manager;
+    let log_dir = app_handle.path().app_log_dir().map_err(|e| e.to_string())?;
+    let log_file = log_dir.join("firelink.log");
+    let src = if log_file.exists() {
+        log_file
+    } else {
+        let mut found = None;
+        if let Ok(mut entries) = tokio::fs::read_dir(&log_dir).await {
+            while let Ok(Some(entry)) = entries.next_entry().await {
+                if entry.path().extension().is_some_and(|e| e == "log") {
+                    found = Some(entry.path());
+                    break;
+                }
+            }
+        }
+        found.ok_or_else(|| "No log file found in app log directory".to_string())?
+    };
+    tokio::fs::copy(&src, &dest_path).await.map_err(|e| e.to_string())?;
+    Ok(dest_path)
+}
+
 #[tauri::command]
 fn toggle_tray_icon(app_handle: tauri::AppHandle, show: bool) -> Result<(), String> {
     use tauri::tray::TrayIconBuilder;
@@ -1785,6 +1808,15 @@ pub fn run() {
                     tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::Webview),
                 ])
                 .level(if cfg!(debug_assertions) { log::LevelFilter::Debug } else { log::LevelFilter::Info })
+                .max_file_size(10_000_000)
+                .rotation_strategy(tauri_plugin_log::RotationStrategy::KeepSome(3))
+                .format(move |out, message, _record| {
+                    let msg = message.to_string();
+                    if msg.contains("[download]") && msg.contains('%') {
+                        return;
+                    }
+                    out.finish(format_args!("{}\n", msg));
+                })
                 .build(),
         )
         .plugin(tauri_plugin_store::Builder::new().build())
@@ -1811,7 +1843,8 @@ pub fn run() {
             enqueue_download, enqueue_many, move_in_queue, remove_from_queue, get_pending_order,
             commands::reveal_in_file_manager, commands::open_downloaded_file, commands::trash_download_assets,
             parity::get_system_proxy, parity::get_file_category, parity::check_for_updates, parity::is_supported_media, parity::get_supported_media_domains,
-            parity::create_category_directories
+            parity::create_category_directories,
+            export_logs
         ])
         .build(tauri::generate_context!())
         .expect("error while building tauri application")