feat(call): enhance call handling with error differentiation and online notifications

- Added error handling for call invite and answer processes to differentiate between callee offline and call already answered scenarios.
- Introduced a new method to publish messages only to online users, improving real-time communication during call signaling.
- Updated call service to check callee's online status before sending call invites, ensuring better user experience.
- Enhanced call acceptance logic to notify both caller and callee about call status changes, including when a call is answered on another device.

internal/handler/ws_handler.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"strconv"
@@ -466,6 +467,15 @@ func (h *WSHandler) handleCallInvite(ctx context.Context, client *ws.Client, pay
 			zap.String("callee_id", req.CalleeID),
 			zap.Error(err),
 		)
+		// === 区分不同错误类型 ===
+		if errors.Is(err, service.ErrCalleeOffline) {
+			h.wsHub.SendError(client, "callee_offline", "对方当前离线，无法拨打")
+			return
+		}
+		if errors.Is(err, service.ErrCallInProgress) {
+			h.wsHub.SendError(client, "call_in_progress", err.Error())
+			return
+		}
 		h.wsHub.SendError(client, "call_invite_failed", err.Error())
 		return
 	}
@@ -499,6 +509,11 @@ func (h *WSHandler) handleCallAnswer(ctx context.Context, client *ws.Client, pay
 
 	call, err := h.callService.Accept(ctx, req.CallID, client.UserID)
 	if err != nil {
+		// === 区分已接听错误 ===
+		if errors.Is(err, service.ErrCallAlreadyAnswered) {
+			h.wsHub.SendError(client, "call_already_answered", "通话已被其他设备接听")
+			return
+		}
 		h.wsHub.SendError(client, "call_accept_failed", err.Error())
 		return
 	}