ax(mining): rename minersMu to minersMutex in wsClient

AX Principle 1: predictable names over short names. The abbreviated
field minersMu was missed when the EventHub mu was renamed to mutex
in a prior sweep.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/events.go

@@ -60,7 +60,7 @@ type wsClient struct {
 	send      chan []byte
 	hub       *EventHub
 	miners    map[string]bool // subscribed miners, "*" for all
-	minersMu  sync.RWMutex    // protects miners map from concurrent access
+	minersMutex sync.RWMutex // protects miners map from concurrent access
 	closeOnce sync.Once
 }
 
@@ -208,8 +208,8 @@ func (h *EventHub) shouldSendToClient(client *wsClient, event Event) bool {
 	}
 
 	// Check miner subscription for miner events (protected by mutex)
-	client.minersMu.RLock()
-	defer client.minersMu.RUnlock()
+	client.minersMutex.RLock()
+	defer client.minersMutex.RUnlock()
 
 	if client.miners == nil || len(client.miners) == 0 {
 		// No subscription filter, send all
@@ -359,12 +359,12 @@ func (c *wsClient) readPump() {
 		switch msg.Type {
 		case "subscribe":
 			// Update miner subscription (protected by mutex)
-			c.minersMu.Lock()
+			c.minersMutex.Lock()
 			c.miners = make(map[string]bool)
 			for _, m := range msg.Miners {
 				c.miners[m] = true
 			}
-			c.minersMu.Unlock()
+			c.minersMutex.Unlock()
 			logging.Debug("client subscribed to miners", logging.Fields{"miners": msg.Miners})
 
 		case "ping":