feat(delivery): implement delivery scheduler and state machine

Core delivery service with: task creation (idempotent, validated),
background scheduler (claimAndReserve with SELECT FOR UPDATE SKIP
LOCKED), 4-level concurrency control, resource quota enforcement,
host allocation from candidate pool, AWX job dispatch, polling,
TCP health check, instance registration, CloudDM integration
(optional), and cancel support. 11-state machine with optimistic
locking and full event audit trail.

Relates-to: #97

server/internal/service/delivery_test.go

@@ -0,0 +1,27 @@
+package service
+
+import "testing"
+
+func TestValidateDeliveryInput(t *testing.T) {
+	valid := MySQLDeliveryInput{BusinessLineID: 1, TargetID: 1, Namespace: "team-a", InstanceName: "mysql-01", CPUMilli: 500, MemoryMi: 1024, StorageGi: 10}
+	if err := validateDeliveryInput(valid); err != nil {
+		t.Fatalf("valid input rejected: %v", err)
+	}
+	for name, input := range map[string]MySQLDeliveryInput{
+		"uppercase namespace": valid,
+		"bad instance":        valid,
+		"too little memory":   valid,
+	} {
+		switch name {
+		case "uppercase namespace":
+			input.Namespace = "Team-A"
+		case "bad instance":
+			input.InstanceName = "mysql_01"
+		case "too little memory":
+			input.MemoryMi = 128
+		}
+		if err := validateDeliveryInput(input); err == nil {
+			t.Errorf("%s was accepted", name)
+		}
+	}
+}