feat(03-01): HookEvent struct, processHookEvent mapping, UpdateFromHook, WaitType

- HookEvent struct parses Claude Code hook JSON payload
- processHookEvent maps Notification/Stop/PostToolUse/PreToolUse to State+WaitType
- UpdateFromHook creates new entries and manages WaitingSince transitions
- SessionInfo.WaitType serialized in JSON with omitempty
- 12 tests cover all event mappings, edge cases, and JSON serialization

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

protocol_test.go

@@ -101,3 +101,49 @@ func TestResponseWithSessions(t *testing.T) {
 		t.Error("waiting_since = nil, want non-nil")
 	}
 }
+
+func TestSessionInfoWaitTypeJSON(t *testing.T) {
+	// WaitType="permission" should appear in JSON
+	info := SessionInfo{
+		SessionID: "sess-1",
+		State:     "Needs Input",
+		WaitType:  "permission",
+	}
+
+	data, err := json.Marshal(info)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+
+	var m map[string]interface{}
+	if err := json.Unmarshal(data, &m); err != nil {
+		t.Fatalf("unmarshal map: %v", err)
+	}
+
+	if wt, ok := m["wait_type"]; !ok {
+		t.Error("wait_type field missing from JSON")
+	} else if wt != "permission" {
+		t.Errorf("wait_type = %v, want %q", wt, "permission")
+	}
+
+	// WaitType="" should be omitted (omitempty)
+	info2 := SessionInfo{
+		SessionID: "sess-2",
+		State:     "Working",
+		WaitType:  "",
+	}
+
+	data2, err := json.Marshal(info2)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+
+	var m2 map[string]interface{}
+	if err := json.Unmarshal(data2, &m2); err != nil {
+		t.Fatalf("unmarshal map: %v", err)
+	}
+
+	if _, ok := m2["wait_type"]; ok {
+		t.Error("wait_type should be omitted when empty")
+	}
+}