Add event-driven daemon architecture (Phase 1 foundation)

- Add fsnotify dependency for file watching
- Create daemon_debouncer.go: batch rapid events (500ms window)
- Create daemon_watcher.go: monitor JSONL and git refs changes
- Create daemon_event_loop.go: event-driven sync loop
- Add mutation channel to RPC server (create/update/close events)
- Add BEADS_DAEMON_MODE env var (poll/events, default: poll)

Phase 1 implementation: opt-in via BEADS_DAEMON_MODE=events
Target: <500ms latency (vs 5000ms), ~60% CPU reduction

Related: bd-49 (epic), bd-50, bd-51, bd-53, bd-54, bd-55, bd-56
Amp-Thread-ID: https://ampcode.com/threads/T-35a3d0d7-4e19-421d-8392-63755035036e
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/server_issues_epics.go

@@ -159,6 +159,9 @@ func (s *Server) handleCreate(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("create", issue.ID)
+
 	data, _ := json.Marshal(issue)
 	return Response{
 		Success: true,
@@ -190,6 +193,9 @@ func (s *Server) handleUpdate(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("update", updateArgs.ID)
+
 	issue, err := store.GetIssue(ctx, updateArgs.ID)
 	if err != nil {
 		return Response{
@@ -224,6 +230,9 @@ func (s *Server) handleClose(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("update", closeArgs.ID)
+
 	issue, _ := store.GetIssue(ctx, closeArgs.ID)
 	data, _ := json.Marshal(issue)
 	return Response{