fix: use proper Monitor constructor in PMG tests to initialize all maps

Fixes panic: assignment to entry in nil map in PMG polling tests.

**Problem:**
Tests were manually creating Monitor structs without initializing internal
maps like pollStatusMap, causing nil map panics when recordTaskResult()
tried to update task status.

**Root Cause:**
- TestPollPMGInstancePopulatesState (line 90)
- TestPollPMGInstanceRecordsAuthFailures (line 189)

Both created Monitor with only partial field initialization, missing:
- pollStatusMap
- dlqInsightMap
- instanceInfoCache
- Other internal state maps

**Solution:**
Changed both tests to use New() constructor which properly initializes all
maps and internal state (monitor.go:1541). This ensures tests match production
initialization and will automatically pick up any future map additions.

**Tests:**
✅ TestPollPMGInstancePopulatesState - now passes
✅ TestPollPMGInstanceRecordsAuthFailures - now passes
✅ All monitoring tests pass (0.125s)

Follows best practice: use constructors instead of manual struct creation
to maintain initialization invariants.

internal/monitoring/monitor_pmg_test.go

@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"github.com/rcourtman/pulse-go-rewrite/internal/config"
-	"github.com/rcourtman/pulse-go-rewrite/internal/models"
 	"github.com/rcourtman/pulse-go-rewrite/pkg/pmg"
 )
 
@@ -87,8 +86,7 @@ func TestPollPMGInstancePopulatesState(t *testing.T) {
 		t.Fatalf("unexpected client error: %v", err)
 	}
 
-	mon := &Monitor{
+	cfg := &config.Config{
-		config: &config.Config{
 		PMGInstances: []config.PMGInstance{
 			{
 				Name:               "primary",
@@ -101,11 +99,11 @@ func TestPollPMGInstancePopulatesState(t *testing.T) {
 				MonitorDomainStats: true,
 			},
 		},
-		},
+	}
-		state:            models.NewState(),
+
-		authFailures:     make(map[string]int),
+	mon, err := New(cfg)
-		lastAuthAttempt:  make(map[string]time.Time),
+	if err != nil {
-		pbsBackupPollers: make(map[string]bool),
+		t.Fatalf("failed to create monitor: %v", err)
 	}
 
 	mon.pollPMGInstance(context.Background(), "primary", client)
@@ -187,8 +185,7 @@ func TestPollPMGInstanceRecordsAuthFailures(t *testing.T) {
 		t.Fatalf("unexpected error creating token client: %v", err)
 	}
 
-	mon := &Monitor{
+	cfg := &config.Config{
-		config: &config.Config{
 		PMGInstances: []config.PMGInstance{
 			{
 				Name:       "failing",
@@ -198,11 +195,11 @@ func TestPollPMGInstanceRecordsAuthFailures(t *testing.T) {
 				TokenValue: "secret",
 			},
 		},
-		},
+	}
-		state:            models.NewState(),
+
-		authFailures:     make(map[string]int),
+	mon, err := New(cfg)
-		lastAuthAttempt:  make(map[string]time.Time),
+	if err != nil {
-		pbsBackupPollers: make(map[string]bool),
+		t.Fatalf("failed to create monitor: %v", err)
 	}
 
 	mon.pollPMGInstance(context.Background(), "failing", client)