Show image names in vm list and raise default memory

Make `banger vm list` easier to scan by resolving each VM image ID back to the registered image name when that mapping is available, while still falling back to a short ID for unknown images.

Raise the shared default VM memory from 1024 MiB to 2048 MiB so new VMs, CLI help, and daemon-side defaults all align on a 2 GiB baseline.

Add CLI coverage for the image-name rendering path and validate the change with go test ./..., make build, `banger vm list`, and `banger vm create --help`.

internal/model/types.go

@@ -17,7 +17,7 @@ const (
 	DefaultDNS                       = "1.1.1.1"
 	DefaultSystemOverlaySize         = 8 * 1024 * 1024 * 1024
 	DefaultWorkDiskSize              = 8 * 1024 * 1024 * 1024
-	DefaultMemoryMiB                 = 1024
+	DefaultMemoryMiB                 = 2048
 	DefaultVCPUCount                 = 2
 	DefaultStatsPollInterval         = 10 * time.Second
 	DefaultStaleSweepInterval        = 1 * time.Minute