Read a path or URL named help or h as an argument (closes #198)

On gen, check, freshen, fetch, list and export, a first argument of
`help` or `h` ran urfave/cli's built-in help command, so
`check help --require-signature FPR` printed help and passed. Those
commands now set urfave/cli's HideHelpCommand, which leaves out their
help command; the root keeps its own, so `mfer help` and
`mfer help check` still work. `check DIR --help` failed with
`No help topic for 'DIR'`; their CommandNotFound now prints the
command's own help, as `check --help` does.

Model: opus-5-5

internal/cli/entry_test.go

@@ -1860,28 +1860,33 @@ func TestCommandsReadHelpAsArgument(t *testing.T) {
 	}
 }
 
-// TestCheckHelpBesideArgument runs check with --help or -h before and after
-// a directory, and runs help check. Each must print what check --help prints.
-func TestCheckHelpBesideArgument(t *testing.T) {
+// TestHelpBesideArgument runs each command that takes a path or URL with
+// --help or -h before and after a directory, and runs help on that command.
+// Each must print what the command's own --help prints.
+func TestHelpBesideArgument(t *testing.T) {
 	t.Parallel()
 
-	want := testOpts([]string{testApp, cmdCheck, testFlagHelp}, afero.NewMemMapFs())
-	require.Equal(t, 0, runCLI(want))
-	require.Contains(t, testStdout(t, want), "Validate files using manifest file")
-
-	for _, args := range [][]string{
-		{cmdCheck, testDir, testFlagHelp},
-		{cmdCheck, testFlagHelp, testDir},
-		{cmdCheck, testDir, "-h"},
-		{testCmdHelp, cmdCheck},
+	for _, command := range []string{
+		cmdGenerate, cmdCheck, cmdFreshen, cmdList, cmdExport, cmdFetch,
 	} {
-		t.Run(strings.Join(args, " "), func(t *testing.T) {
-			t.Parallel()
+		want := testOpts([]string{testApp, command, testFlagHelp}, afero.NewMemMapFs())
+		require.Equal(t, 0, runCLI(want))
+		require.Contains(t, testStdout(t, want), testApp+" "+command)
 
-			opts := testOpts(slices.Concat([]string{testApp}, args), afero.NewMemMapFs())
-			assert.Equal(t, 0, runCLI(opts), testStderr(t, opts))
-			assert.Equal(t, testStdout(t, want), testStdout(t, opts))
-		})
+		for _, args := range [][]string{
+			{command, testDir, testFlagHelp},
+			{command, testFlagHelp, testDir},
+			{command, testDir, "-h"},
+			{testCmdHelp, command},
+		} {
+			t.Run(strings.Join(args, " "), func(t *testing.T) {
+				t.Parallel()
+
+				opts := testOpts(slices.Concat([]string{testApp}, args), afero.NewMemMapFs())
+				assert.Equal(t, 0, runCLI(opts), testStderr(t, opts))
+				assert.Equal(t, testStdout(t, want), testStdout(t, opts))
+			})
+		}
 	}
 }