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>

app/src-tauri/src/bridge.rs

@@ -430,6 +430,11 @@ pub async fn mark_read(state: BridgeState<'_>, target: Value) -> Result<Value, S
     data_of(state.request(Cmd::MarkRead { target }).await.map_err(|e| e.to_string())?)
 }
 
+#[tauri::command]
+pub async fn clear_events(state: BridgeState<'_>) -> Result<Value, String> {
+    data_of(state.request(Cmd::ClearEvents).await.map_err(|e| e.to_string())?)
+}
+
 #[tauri::command]
 pub async fn health(state: BridgeState<'_>) -> Result<Value, String> {
     data_of(state.request(Cmd::Health).await.map_err(|e| e.to_string())?)