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/status.go

@@ -34,16 +34,16 @@ type StatusCommand struct {
 }
 
 func (c *StatusCommand) Synopsis() string {
-	return "Get the status information of the running boundary cache"
+	return "Get the status information of the running threshold cache"
 }
 
 func (c *StatusCommand) Help() string {
 	helpText := `
-Usage: boundary cache status [options]
+Usage: threshold cache status [options]
 
-  Get the status of the boundary cache:
+  Get the status of the threshold cache:
 
-      $ boundary cache status
+      $ threshold cache status
 
   For a full list of examples, please see the documentation.