fix(daemon): restore slog default after viperblock.New mutates it

viperblock.New unconditionally calls vb.SetDebug, which calls
slog.SetDefault with a TextHandler at LevelError — globally silencing
every slog.Info and slog.Warn in the caller process for the rest of
its life. Discovered while validating microvm Phase 2 (mulga-siv-68):
the daemon stopped emitting Info logs the moment the first customer
VM with volumes launched, hiding direct-boot timing,
LaunchSystemInstance completed, and CreateLoadBalancer completed
lines that we need for boot-time tuning.

Workaround in newViperblock: re-install an Info-level TextHandler on
os.Stderr after each viperblock.New call. Also drop the three explicit
vb.SetDebug(false) calls in prepareRootVolume / prepareEFIVolume /
prepareCloudInitVolume — they were no-ops (viperblock.New already
runs SetDebug internally) and each one re-triggered the global
mutation we are trying to undo.

Proper fix is in viperblock itself — tracked as mulga-siv-70: SetDebug
should not call slog.SetDefault. Until then, this restore call is the
shortest path to getting the daemon's observability back so we can
measure t1_to_t2_ms and tune Phase 2.

Preflight note: golangci-lint not available on this dev host, so the
project preflight target cannot run end-to-end. Verified with
go vet ./spinifex/handlers/ec2/instance/... (clean) and
go test ./spinifex/handlers/ec2/instance/... (pass).

spinifex/handlers/ec2/instance/service_impl.go

@@ -877,7 +877,20 @@ func (s *InstanceServiceImpl) newViperblock(volumeName string, size int, volumeC
 		VolumeConfig: volumeConfig,
 	}
 
-	return viperblock.New(&vbconfig, "s3", cfg)
+	vb, err := viperblock.New(&vbconfig, "s3", cfg)
+	restoreSlogDefault()
+	return vb, err
+}
+
+// restoreSlogDefault re-installs the daemon's Info-level slog handler after
+// viperblock.New mutates the global slog default via its SetDebug method
+// (see viperblock.go SetDebug — it calls slog.SetDefault with LevelError,
+// silencing every Info/Warn in the entire process). Tracked for proper fix
+// in viperblock as mulga-siv-70.
+func restoreSlogDefault() {
+	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	})))
 }
 
 // prepareRootVolume handles creation/cloning of the root volume
@@ -888,8 +901,6 @@ func (s *InstanceServiceImpl) prepareRootVolume(input *ec2.RunInstancesInput, im
 		return errors.New(awserrors.ErrorServerInternal)
 	}
 
-	vb.SetDebug(false)
-
 	// Initialize the backend
 	err = vb.Backend.Init()
 	if err != nil {
@@ -996,8 +1007,6 @@ func (s *InstanceServiceImpl) prepareEFIVolume(imageId string, volumeConfig vipe
 		return errors.New(awserrors.ErrorServerInternal)
 	}
 
-	efiVb.SetDebug(false)
-
 	// Initialize the backend
 	slog.Debug("Initializing EFI Viperblock store backend")
 	err = efiVb.Backend.Init()
@@ -1083,8 +1092,6 @@ func (s *InstanceServiceImpl) prepareCloudInitVolume(input *ec2.RunInstancesInpu
 		return errors.New(awserrors.ErrorServerInternal)
 	}
 
-	cloudInitVb.SetDebug(false)
-
 	// Initialize the backend
 	slog.Debug("Initializing cloud-init Viperblock store backend")
 	err = cloudInitVb.Backend.Init()