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/releases.go

@@ -307,7 +307,7 @@ $ tea release create v1.1.0-rc1 --target release/1.1 --draft --prerelease --titl
 	command.Flags().StringVar(&fields.tag, "tag", "", "Release tag")
 	_ = command.Flags().MarkHidden("tag")
 	command.Flags().StringSliceVar(&assets, "asset", nil, "File to upload as an asset (repeatable)")
-	command.ValidArgsFunction = a.completeTags()
+	command.ValidArgsFunction = pathArgs(1, true, completeFiles, a.completeTags())
 	return command
 }