ax(mining): replace prose comments with usage examples in simulated_miner.go

AX Principle 2: comments must show concrete usage, not restate the signature.
Four functions (NewSimulatedMiner, Stop, GetStats, SimulatedMinerPresets) had
"X does Y" prose descriptions replaced with call-site examples.

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

pkg/mining/simulated_miner.go

@@ -52,7 +52,8 @@ type SimulatedMinerConfig struct {
 	Difficulty   int     // Base difficulty
 }
 
-// NewSimulatedMiner creates a new simulated miner instance.
+// miner := NewSimulatedMiner(SimulatedMinerConfig{Name: "sim-001", Algorithm: "rx/0", BaseHashrate: 5000})
+// miner.Start(ctx)
 func NewSimulatedMiner(config SimulatedMinerConfig) *SimulatedMiner {
 	if config.Variance <= 0 {
 		config.Variance = 0.1 // Default 10% variance
@@ -125,7 +126,7 @@ func (m *SimulatedMiner) Start(config *Config) error {
 	return nil
 }
 
-// Stop stops the simulated miner.
+// if err := miner.Stop(); err != nil { /* miner was not running */ }
 func (m *SimulatedMiner) Stop() error {
 	m.mu.Lock()
 	defer m.mu.Unlock()
@@ -264,7 +265,8 @@ func (m *SimulatedMiner) simulateShare() {
 	}
 }
 
-// GetStats returns current performance metrics.
+// metrics, err := miner.GetStats(ctx)
+// fmt.Printf("hashrate: %d H/s, shares: %d\n", metrics.Hashrate, metrics.Shares)
 func (m *SimulatedMiner) GetStats(ctx context.Context) (*PerformanceMetrics, error) {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
@@ -417,7 +419,8 @@ func (m *SimulatedMiner) WriteStdin(input string) error {
 	return nil
 }
 
-// SimulatedMinerPresets provides common presets for simulated miners.
+// miner := NewSimulatedMiner(SimulatedMinerPresets["cpu-medium"])
+// miner := NewSimulatedMiner(SimulatedMinerPresets["gpu-ethash"])
 var SimulatedMinerPresets = map[string]SimulatedMinerConfig{
 	"cpu-low": {
 		Algorithm:    "rx/0",