Prompt for workspace ID when workspace list fails (#4859)

## Summary
- When `databricks auth login` fails to fetch the workspace list (e.g.
user lacks account-level permissions), prompt the user to manually enter
a workspace ID instead of logging and error and skipping the workspace
selection.
- Empty input skips workspace selection to support account only
profiles.

## Manual test

```
$ ./cli auth login --host https://db-deco-test.databricks.com/        
Databricks profile name [db-deco-test]: 
Profile db-deco-test was successfully saved

$ ./cli auth login --host https://dogfood.staging.databricks.com/        
Databricks profile name [dogfood]: 
Warn: Failed to load workspaces (this can happen if the user has no account-level access): Invalid Token
Enter workspace ID (empty to skip): 123
Profile dogfood was successfully saved
```

## Test plan
- [x] Manually tested with a host where workspace listing fails (no
account-level access)
- [x] Manually tested with a host where workspace listing succeeds (no
change in behavior)

This pull request was AI-assisted by Isaac.

---------

Co-authored-by: Renaud Hartert <renaud.hartert@databricks.com>

Author: hectorcast-db

cmd/auth/login.go

@@ -725,7 +725,8 @@ func promptForWorkspaceSelection(ctx context.Context, authArguments *auth.AuthAr
 
 	workspaces, err := a.Workspaces.List(ctx)
 	if err != nil {
-		return "", err
+		log.Debugf(ctx, "Failed to load workspaces (this can happen if the user has no account-level access): %v", err)
+		return promptForWorkspaceID(ctx)
 	}
 
 	if len(workspaces) == 0 {
@@ -764,6 +765,19 @@ func promptForWorkspaceSelection(ctx context.Context, authArguments *auth.AuthAr
 	return selected, nil
 }
 
+// promptForWorkspaceID asks the user to manually enter a workspace ID.
+// Returns empty string if the user provides no input.
+func promptForWorkspaceID(ctx context.Context) (string, error) {
+	prompt := cmdio.Prompt(ctx)
+	prompt.Label = "Enter workspace ID (empty to skip)"
+	prompt.AllowEdit = true
+	result, err := prompt.Run()
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(result), nil
+}
+
 // getBrowserFunc returns a function that opens the given URL in the browser.
 // It respects the BROWSER environment variable:
 // - empty string: uses the default browser