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/spacesh-proto/src/message.rs

@@ -124,6 +124,7 @@ pub enum Cmd {
         limit: Option<u32>,
     },
     MarkRead { target: MarkReadTarget },
+    ClearEvents,
     SetZoom {
         workspace_id: WorkspaceId,
         #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -163,6 +164,7 @@ pub enum Evt {
     State { surface_id: SurfaceId, state: SurfaceState },
     Event { record: EventRecord },
     EventsRead { ids: Vec<u64> },
+    EventsCleared,
     ConfigChanged { config: crate::config_view::ConfigView },
 }