Add test notification endpoint and UI button

- Add POST /api/test-notification endpoint to send test to saved config URL
- Refactor send_notification to return Result instead of bool
- Add NotificationError enum for proper error handling
- Add test notification button in config UI with explanatory text
- Button tests saved configuration URL, not input field value

daemon/src/main.rs

@@ -23,6 +23,7 @@ use crate::pcap::get_pcap;
 use crate::qmdl_store::RecordingStore;
 use crate::server::{
     ServerState, debug_set_display_state, get_config, get_qmdl, get_zip, serve_static, set_config,
+    test_notification,
 };
 use crate::stats::{get_qmdl_manifest, get_system_stats};
 
@@ -68,6 +69,7 @@ fn get_router() -> AppRouter {
         .route("/api/analysis/{name}", post(start_analysis))
         .route("/api/config", get(get_config))
         .route("/api/config", post(set_config))
+        .route("/api/test-notification", post(test_notification))
         .route("/api/debug/display-state", post(debug_set_display_state))
         .route("/", get(|| async { Redirect::permanent("/index.html") }))
         .route("/{*path}", get(serve_static))