Add flag to auto-navigate to new worktree after creation

[fmal]

Feature Request

When creating a new worktree with gwtr new my-feature, I always end up running gwtr cd my-feature immediately after. It would be great to have a flag (e.g. --cd or --navigate) that automatically changes into the new worktree directory after creation.

Current workflow

gwtr new my-feature
gwtr cd my-feature

Desired workflow

gwtr new my-feature --cd
# already in the new worktree directory

Context

I don't use the --editor or --ai flags — I just want a quick way to create and land in the new worktree in one step. This seems like a common enough pattern that a dedicated flag (or even a config default) would be useful.