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/cmd/commands/database/database.go

@@ -19,18 +19,18 @@ type Command struct {
 }
 
 func (c *Command) Synopsis() string {
-	return "Manage Boundary's database"
+	return "Manage Threshold's database"
 }
 
 func (c *Command) Help() string {
 	return base.WrapForHelpText([]string{
-		"Usage: boundary database [sub command] [options] [args]",
+		"Usage: threshold database [sub command] [options] [args]",
 		"",
-		"  This command allows operations on Boundary's database. Example:",
+		"  This command allows operations on Threshold's database. Example:",
 		"",
 		"    Initialize the database:",
 		"",
-		`      $ boundary database init`,
+		`      $ threshold database init`,
 		"",
 		"  Please see the database subcommand help for detailed usage information.",
 	})