feat(daemon): EventLog ring model with read-flags

Add event_log.rs with EventLog (capped VecDeque, monotonic ids, mark_read,
snapshot/restore) and EventLogState. Register mod in main.rs. Stub
Cmd::EventLog and Cmd::MarkRead arms in server.rs to keep the exhaustive
match compiling; full wiring follows in Task 4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/spaceshd/src/server.rs

@@ -526,6 +526,18 @@ async fn handle_request(
             let _ = out.send(ok(id, serde_json::json!({ "groups": groups, "workspaces": workspaces }))).await;
         }
 
+        Cmd::EventLog { limit } => {
+            // TODO(SP2-T4): wire to EventLog once the shared state is plumbed in.
+            let _ = limit;
+            let _ = out.send(err(id, "NOT_IMPLEMENTED", "event log not yet wired")).await;
+        }
+
+        Cmd::MarkRead { target } => {
+            // TODO(SP2-T4): wire to EventLog once the shared state is plumbed in.
+            let _ = target;
+            let _ = out.send(err(id, "NOT_IMPLEMENTED", "mark_read not yet wired")).await;
+        }
+
         Cmd::Shutdown => {
             let _ = out.send(ok(id, serde_json::Value::Null)).await;
             std::process::exit(0);