feat: add server_restart WebSocket message type for update notifications

Server/ws/hub.go

@@ -98,6 +98,13 @@ func (h *Hub) BroadcastToAll(msg []byte) {
 	h.broadcast <- broadcastMsg{channelID: 0, msg: msg}
 }
 
+// BroadcastServerRestart sends a server_restart message to all connected clients.
+// reason describes why the server is restarting (e.g., "update").
+// delaySeconds tells clients how long until the server actually shuts down.
+func (h *Hub) BroadcastServerRestart(reason string, delaySeconds int) {
+	h.BroadcastToAll(buildServerRestartMsg(reason, delaySeconds))
+}
+
 // SendToUser delivers msg directly to the client identified by userID.
 // Returns true if the client was found and the message was queued.
 func (h *Hub) SendToUser(userID int64, msg []byte) bool {

Server/ws/messages.go

@@ -178,6 +178,17 @@ func buildSoundboardPlay(soundID string, userID int64) []byte {
 	})
 }
 
+// buildServerRestartMsg constructs a server_restart broadcast.
+func buildServerRestartMsg(reason string, delaySeconds int) []byte {
+	return buildJSON(map[string]interface{}{
+		"type": "server_restart",
+		"payload": map[string]interface{}{
+			"reason":        reason,
+			"delay_seconds": delaySeconds,
+		},
+	})
+}
+
 // parseChannelID safely extracts channel_id from a raw payload map.
 func parseChannelID(payload json.RawMessage) (int64, error) {
 	var p struct {

Server/ws/messages_test.go

@@ -0,0 +1,29 @@
+package ws
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestBuildServerRestartMsg(t *testing.T) {
+	msg := buildServerRestartMsg("update", 5)
+	var env struct {
+		Type    string `json:"type"`
+		Payload struct {
+			Reason       string `json:"reason"`
+			DelaySeconds int    `json:"delay_seconds"`
+		} `json:"payload"`
+	}
+	if err := json.Unmarshal(msg, &env); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if env.Type != "server_restart" {
+		t.Errorf("type = %q, want server_restart", env.Type)
+	}
+	if env.Payload.Reason != "update" {
+		t.Errorf("reason = %q, want update", env.Payload.Reason)
+	}
+	if env.Payload.DelaySeconds != 5 {
+		t.Errorf("delay_seconds = %d, want 5", env.Payload.DelaySeconds)
+	}
+}