refactor(completion): name path arguments explicitly and share firstArg

The six commands that take a file or directory argument set their
completer directly instead of a Use-line parser wrapping every
command, the first-argument-only wrappers become one firstArg helper,
and only the bash completion help keeps a custom text.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/release_assets.go

@@ -154,7 +154,7 @@ $ tea release upload v1.0.0 dist/tea-linux --clobber`,
 	}
 	command.Flags().StringVar(&name, "name", "", "Asset name (default: the file's name)")
 	command.Flags().BoolVar(&clobber, "clobber", false, "Replace assets with the same name")
-	command.ValidArgsFunction = a.completeReleases()
+	command.ValidArgsFunction = pathArgs(1, true, completeFiles, a.completeReleases())
 	return command
 }