[feat:extensions] add support to package web-bot-auth (#62)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Adds a new CLI flow to fetch, build, and package Cloudflare’s
`web-bot-auth` browser extension with Kernel-specific configs, plus
supporting utils and tests.
> 
> - New `kernel extensions build-web-bot-auth` command in
`cmd/extensions.go` with flags `--to`, `--url`, `--key`, `--upload`; can
auto-upload to Kernel under a specified name
> - Implements build pipeline in `pkg/extensions/webbotauth.go`:
downloads GitHub archive, validates/converts Ed25519 keys (JWK/PEM),
modifies policy/build templates, runs `npm install/build/bundle`,
extracts extension ID, and copies artifacts (`.crx`, `update.xml`,
`policy`, built files) to output
> - Adds crypto helpers in `pkg/util/crypto.go` (`ValidatePEMKey`,
`IsPEMKey`, `ConvertJWKToPEM`) and file ops in `pkg/util/fileops.go`
(`CopyFile`, `CopyDir`, `ModifyFile`)
> - New tests: download/extract integration in
`pkg/extensions/webbotauth_test.go` and crypto unit tests in
`pkg/util/crypto_test.go`
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
5268e7a. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: archandatta

cmd/extensions.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"time"
 
+	"github.com/kernel/cli/pkg/extensions"
 	"github.com/kernel/cli/pkg/util"
 	"github.com/kernel/kernel-go-sdk"
 	"github.com/kernel/kernel-go-sdk/option"
@@ -422,12 +423,60 @@ var extensionsUploadCmd = &cobra.Command{
 	},
 }
 
+var extensionsBuildWebBotAuthCmd = &cobra.Command{
+	Use:   "build-web-bot-auth",
+	Short: "Build the Cloudflare web-bot-auth extension for Kernel",
+	Long: `Download, build, and prepare the Cloudflare web-bot-auth extension with Kernel-specific configurations.
+					Defaults to RFC9421 test key (works with Cloudflare's test site).
+					Uploads it to Kernel as 'web-bot-auth'. Optionally accepts a custom JWK or PEM key file.`,
+	Args: cobra.NoArgs,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		output, _ := cmd.Flags().GetString("to")
+		url, _ := cmd.Flags().GetString("url")
+		keyPath, _ := cmd.Flags().GetString("key")
+		uploadName, _ := cmd.Flags().GetString("upload")
+
+		// Use upload name for extension name, or default to "web-bot-auth"
+		extensionName := "web-bot-auth"
+		if uploadName != "" {
+			extensionName = uploadName
+		}
+
+		// Build the extension
+		result, err := extensions.BuildWebBotAuth(cmd.Context(), extensions.ExtensionsBuildWebBotAuthInput{
+			Output:        output,
+			HostURL:       url,
+			KeyPath:       keyPath,
+			ExtensionName: extensionName,
+			AutoUpload:    uploadName != "",
+		})
+		if err != nil {
+			return err
+		}
+
+		// Upload if requested
+		if uploadName != "" {
+			client := getKernelClient(cmd)
+			svc := client.Extensions
+			e := ExtensionsCmd{extensions: &svc}
+			pterm.Info.Println("Uploading extension to Kernel...")
+			return e.Upload(cmd.Context(), ExtensionsUploadInput{
+				Dir:  result.OutputDir,
+				Name: extensionName,
+			})
+		}
+
+		return nil
+	},
+}
+
 func init() {
 	extensionsCmd.AddCommand(extensionsListCmd)
 	extensionsCmd.AddCommand(extensionsDeleteCmd)
 	extensionsCmd.AddCommand(extensionsDownloadCmd)
 	extensionsCmd.AddCommand(extensionsDownloadWebStoreCmd)
 	extensionsCmd.AddCommand(extensionsUploadCmd)
+	extensionsCmd.AddCommand(extensionsBuildWebBotAuthCmd)
 
 	extensionsListCmd.Flags().StringP("output", "o", "", "Output format: json for raw API response")
 	extensionsDeleteCmd.Flags().BoolP("yes", "y", false, "Skip confirmation prompt")
@@ -436,4 +485,8 @@ func init() {
 	extensionsDownloadWebStoreCmd.Flags().String("os", "", "Target OS: mac, win, or linux (default linux)")
 	extensionsUploadCmd.Flags().StringP("output", "o", "", "Output format: json for raw API response")
 	extensionsUploadCmd.Flags().String("name", "", "Optional unique extension name")
+	extensionsBuildWebBotAuthCmd.Flags().String("to", "./web-bot-auth", "Output directory for the prepared extension")
+	extensionsBuildWebBotAuthCmd.Flags().String("url", "http://127.0.0.1:10001", "Base URL for update.xml and policy templates")
+	extensionsBuildWebBotAuthCmd.Flags().String("key", "", "Path to Ed25519 private key file (JWK or PEM format)")
+	extensionsBuildWebBotAuthCmd.Flags().String("upload", "", "Upload extension to Kernel with specified name (e.g., --upload web-bot-auth)")
 }