feat(app): clear all events from the Event Center (red trash icon)

Adds Cmd::ClearEvents + Evt::EventsCleared: the daemon drops the persistent
event log (keeping next_id monotonic), persists, and broadcasts so every
client empties its list. A red trash icon next to 'Mark all read' triggers it;
disabled when the list is empty. Threaded through proto, the daemon handler,
the Tauri bridge, and socketBridge. Includes an EventLog::clear test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spaceshd/src/server.rs

@@ -648,6 +648,13 @@ async fn handle_request(
             let _ = out.send(ok(id, serde_json::Value::Null)).await;
         }
 
+        Cmd::ClearEvents => {
+            event_log.clear();
+            event_persister.mark_dirty(event_log.snapshot());
+            broadcast_evt(clients, &Envelope::Evt(Evt::EventsCleared));
+            let _ = out.send(ok(id, serde_json::Value::Null)).await;
+        }
+
         Cmd::Shutdown => {
             let _ = out.send(ok(id, serde_json::Value::Null)).await;
             std::process::exit(0);