Remove image build --from-image; doctor treats catalog images as OK

The `image build` flow spun up a transient Firecracker VM, SSHed in,
and ran a large bash provisioning script to derive a new managed
image from an existing one. It overlapped heavily with the golden-
image Dockerfile flow (same mise/docker/tmux/opencode install logic
duplicated in Go as `imagemgr.BuildProvisionScript`) and had far more
machinery: async op state, RPC begin/status/cancel, webui form +
operation page, preflight checks, API types, tests. For custom
images, writing a Dockerfile is simpler and more reproducible.

Removed end-to-end:
- CLI `image build` subcommand + `absolutizeImageBuildPaths`.
- Daemon: BuildImage method, imagebuild.go (transient-VM orchestration),
  image_build_ops.go (async begin/status/cancel), imagemgr/build.go
  (the 247-line provisioning script generator and all its append*
  helpers), validateImageBuildPrereqs + addImageBuildPrereqs.
- RPC dispatches for image.build / .begin / .status / .cancel.
- opstate registry `imageBuildOps`, daemon seam `imageBuild`,
  background pruner call.
- API types: ImageBuildParams, ImageBuildOperation, ImageBuildBeginResult,
  ImageBuildStatusParams, ImageBuildStatusResult; model type
  ImageBuildRequest.
- Web UI: Backend interface methods, handlers, form, routes, template
  branches (images.html build form, operation.html build branch,
  dashboard.html Build button).
- Tests that directly exercised BuildImage.

Doctor polish (task C):
- Drop the "image build" preflight section entirely (its raison d'être
  is gone).
- Default-image check now accepts "not local but in imagecat" as OK:
  vm create auto-pulls on first use. Only flag when the image is
  neither locally registered nor in the catalog.

Net: 24 files touched, 1,373 lines deleted, 25 added.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/banger.go

@@ -1702,7 +1702,6 @@ func newImageCommand() *cobra.Command {
 		RunE:  helpNoArgs,
 	}
 	cmd.AddCommand(
-		newImageBuildCommand(),
 		newImageRegisterCommand(),
 		newImagePullCommand(),
 		newImagePromoteCommand(),
@@ -1713,40 +1712,6 @@ func newImageCommand() *cobra.Command {
 	return cmd
 }
 
-func newImageBuildCommand() *cobra.Command {
-	var params api.ImageBuildParams
-	cmd := &cobra.Command{
-		Use:   "build",
-		Short: "Build an image",
-		Args:  noArgsUsage("usage: banger image build"),
-		RunE: func(cmd *cobra.Command, args []string) error {
-			if err := absolutizeImageBuildPaths(&params); err != nil {
-				return err
-			}
-			if err := system.EnsureSudo(cmd.Context()); err != nil {
-				return err
-			}
-			layout, _, err := ensureDaemon(cmd.Context())
-			if err != nil {
-				return err
-			}
-			result, err := rpc.Call[api.ImageShowResult](cmd.Context(), layout.SocketPath, "image.build", params)
-			if err != nil {
-				return err
-			}
-			return printImageSummary(cmd.OutOrStdout(), result.Image)
-		},
-	}
-	cmd.Flags().StringVar(&params.Name, "name", "", "image name")
-	cmd.Flags().StringVar(&params.FromImage, "from-image", "", "registered base image id or name")
-	cmd.Flags().StringVar(&params.Size, "size", "", "output image size")
-	cmd.Flags().StringVar(&params.KernelPath, "kernel", "", "kernel path")
-	cmd.Flags().StringVar(&params.InitrdPath, "initrd", "", "initrd path")
-	cmd.Flags().StringVar(&params.ModulesDir, "modules", "", "modules dir")
-	cmd.Flags().BoolVar(&params.Docker, "docker", false, "install docker")
-	return cmd
-}
-
 func newImageRegisterCommand() *cobra.Command {
 	var params api.ImageRegisterParams
 	cmd := &cobra.Command{
@@ -3181,10 +3146,6 @@ func shellQuote(value string) string {
 	return "'" + strings.ReplaceAll(value, "'", `'"'"'`) + "'"
 }
 
-func absolutizeImageBuildPaths(params *api.ImageBuildParams) error {
-	return absolutizePaths(&params.KernelPath, &params.InitrdPath, &params.ModulesDir)
-}
-
 func absolutizeImageRegisterPaths(params *api.ImageRegisterParams) error {
 	return absolutizePaths(
 		&params.RootfsPath,

internal/cli/cli_test.go

@@ -1965,40 +1965,6 @@ func TestBuildDaemonCommandIsDetachedFromCallerContext(t *testing.T) {
 	}
 }
 
-func TestAbsolutizeImageBuildPaths(t *testing.T) {
-	dir := t.TempDir()
-	prev, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("getwd: %v", err)
-	}
-	if err := os.Chdir(dir); err != nil {
-		t.Fatalf("chdir: %v", err)
-	}
-	t.Cleanup(func() {
-		_ = os.Chdir(prev)
-	})
-
-	params := api.ImageBuildParams{
-		FromImage:  "base-image",
-		KernelPath: "/kernel",
-		InitrdPath: "boot/initrd.img",
-		ModulesDir: "modules",
-	}
-	if err := absolutizeImageBuildPaths(&params); err != nil {
-		t.Fatalf("absolutizeImageBuildPaths: %v", err)
-	}
-
-	want := api.ImageBuildParams{
-		FromImage:  "base-image",
-		KernelPath: "/kernel",
-		InitrdPath: filepath.Join(dir, "boot/initrd.img"),
-		ModulesDir: filepath.Join(dir, "modules"),
-	}
-	if !reflect.DeepEqual(params, want) {
-		t.Fatalf("params = %+v, want %+v", params, want)
-	}
-}
-
 func testCLIResolvedVM(id, name string) model.VMRecord {
 	return model.VMRecord{ID: id, Name: name}
 }