Count -v once and document -v -v for debug output (closes #125)

urfave/cli before v2.25.5 counted a flag given by its alias twice, so
one -v or --verbose already gave debug output. Bump it to v2.27.7,
which counts it once: one -v gives verbose output, two give debug.

The -v help text now says -v -v instead of -vv, which stays refused:
urfave/cli's option for combined short flags would let a flag that
takes a value read the next letter as its value.

-v and --verbose together stay refused: urfave/cli v2 refuses a flag
given under two of its names, and one flag with an alias keeps help and
parsing simple.

The bump changes some help output; generate and fetch now name their
arguments. Tests start each run at the default log level.

Model: opus-5-5

internal/cli/mfer.go

@@ -17,6 +17,7 @@ import (
 const (
 	cmdGenerate = "generate"
 	cmdCheck    = "check"
+	cmdFreshen  = "freshen"
 	cmdExport   = "export"
 	cmdFetch    = "fetch"
 	cmdVersion  = "version"
@@ -118,7 +119,7 @@ func commonFlags() []cli.Flag {
 		&cli.BoolFlag{
 			Name:    "verbose",
 			Aliases: []string{"v"},
-			Usage:   "Increase verbosity (-v for verbose, -vv for debug)",
+			Usage:   "Increase verbosity (-v for verbose, -v -v for debug)",
 			Count:   new(int),
 		},
 		&cli.BoolFlag{
@@ -131,9 +132,10 @@ func commonFlags() []cli.Flag {
 
 func (mfa *CLIApp) generateCommand() *cli.Command {
 	return &cli.Command{
-		Name:    cmdGenerate,
-		Aliases: []string{"gen"},
-		Usage:   "Generate manifest file",
+		Name:      cmdGenerate,
+		Aliases:   []string{"gen"},
+		Usage:     "Generate manifest file",
+		ArgsUsage: "[path ...]",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()
@@ -227,7 +229,7 @@ func (mfa *CLIApp) checkCommand() *cli.Command {
 
 func (mfa *CLIApp) freshenCommand() *cli.Command {
 	return &cli.Command{
-		Name:      "freshen",
+		Name:      cmdFreshen,
 		Usage:     "Update manifest with changed, new, and removed files",
 		ArgsUsage: manifestArgsUsage,
 		Action: func(c *cli.Context) error {
@@ -324,8 +326,9 @@ func (mfa *CLIApp) listCommand() *cli.Command {
 
 func (mfa *CLIApp) fetchCommand() *cli.Command {
 	return &cli.Command{
-		Name:  cmdFetch,
-		Usage: "fetch manifest and referenced files",
+		Name:      cmdFetch,
+		Usage:     "fetch manifest and referenced files",
+		ArgsUsage: "URL",
 		Action: func(c *cli.Context) error {
 			mfa.setVerbosity(c)
 			mfa.printBanner()