Use sanhook to expose ISO as block device during kernel/initrd boot

The CPIO-embedded initrd approach failed (too large for iPXE memory).
Instead, use iPXE's sanhook to connect the ISO as a SAN block device
before booting with kernel/initrd. The installer finds the ISO on the
SAN device while we retain control over kernel parameters.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/image/service.go

@@ -53,24 +53,8 @@ func (s *Service) Upload(ctx context.Context, p UploadParams) (*model.Image, err
 		return nil, fmt.Errorf("extract ISO: %w", err)
 	}
 
-	report := func(stage, detail string) {
-		if p.OnProgress != nil {
-			p.OnProgress(stage, detail)
-		}
-	}
-	report("packaging", "Creating PXE boot image (embedding ISO in initrd)...")
-
-	origInitrdPath := filepath.Join(destDir, result.InitrdFilename)
-	origISOPath := filepath.Join(destDir, result.ISOFilename)
-	pxeInitrdFile := "initrd-pxe.img"
-	pxeInitrdPath := filepath.Join(destDir, pxeInitrdFile)
-	if err := CreatePXEInitrd(origInitrdPath, origISOPath, pxeInitrdPath); err != nil {
-		os.RemoveAll(destDir)
-		return nil, fmt.Errorf("create PXE initrd: %w", err)
-	}
-
 	kernelPath := filepath.Join(p.Name, result.KernelFilename)
-	initrdPath := filepath.Join(p.Name, pxeInitrdFile)
+	initrdPath := filepath.Join(p.Name, result.InitrdFilename)
 	isoPath := filepath.Join(p.Name, result.ISOFilename)
 
 	id, err := s.Store.Create(ctx, model.Image{