Recompute command path padding when a parent is attached

[AshSgDe29071999]

CommandPathPadding was snapshotted in AddCommand from CommandPath() at that moment. Building a subtree before attaching it to the root used short paths (authentication instead of app remote authentication), so help columns stayed misaligned.

After the parent pointer is set, recompute max lengths down the subtree.

Fixes #2463

Test

go test . -run TestCommandPathPaddingIndependentOfAddOrder -count=1

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