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/cache.go

@@ -21,18 +21,18 @@ type CacheCommand struct {
 }
 
 func (c *CacheCommand) Synopsis() string {
-	return "Manages the client side Boundary cache"
+	return "Manages the client side Threshold cache"
 }
 
 func (c *CacheCommand) Help() string {
 	helpText := `
-Usage: boundary cache [sub command] [options]
+Usage: threshold cache [sub command] [options]
 
-  This command allows interacting with the Boundary cache.
+  This command allows interacting with the Threshold cache.
 
   Start a cache:
 
-      $ boundary cache start
+      $ threshold cache start
 
   For a full list of examples, please see the documentation.
 
@@ -54,7 +54,7 @@ func (c *CacheCommand) AutocompleteFlags() complete.Flags {
 
 func (c *CacheCommand) Run(args []string) int {
 	if len(args) >= 2 && args[1] == "daemon" {
-		c.UI.Warn("The `boundary daemon` command is deprecated, use `boundary cache` instead")
+		c.UI.Warn("The `threshold daemon` command is deprecated, use `threshold cache` instead")
 	}
 	return cli.RunResultHelp
 }