Rebrand user-visible CLI text; add legacy fallbacks for keyring, cache dir and version prefix

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/clientcache/cmd/cache/addtoken.go

@@ -28,16 +28,16 @@ type AddTokenCommand struct {
 }
 
 func (c *AddTokenCommand) Synopsis() string {
-	return "Add an auth token to a running boundary cache"
+	return "Add an auth token to a running threshold cache"
 }
 
 func (c *AddTokenCommand) Help() string {
 	helpText := `
-Usage: boundary cache add-token [options]
+Usage: threshold cache add-token [options]
 
   Add an auth token to the cache:
 
-      $ boundary cache add-token
+      $ threshold cache add-token
 
   For a full list of examples, please see the documentation.
 
@@ -54,7 +54,7 @@ func (c *AddTokenCommand) Flags() *base.FlagSets {
 		Target:     &c.FlagAddr,
 		EnvVar:     api.EnvBoundaryAddr,
 		Completion: complete.PredictAnything,
-		Usage:      "Addr of the Boundary controller, as a complete URL (e.g. https://boundary.example.com:9200).",
+		Usage:      "Addr of the Threshold controller, as a complete URL (e.g. https://threshold.example.com:9200).",
 	})
 
 	f = set.NewFlagSet("Client Options")