* Add `gh stack trunk` navigation command
Add a new navigation command that checks out the trunk branch of the
current stack.
The command is stack-aware: it requires the user to be on a branch that
is part of a stack, loads the stack metadata, and checks out `s.Trunk.Branch`.
If the user is already on the trunk branch, it prints a message and exits
without calling git checkout.
New files:
- cmd/trunk.go: TrunkCmd (cobra command) + runTrunk implementation
- cmd/trunk_test.go: 7 test cases covering happy path, already on
trunk, from top of stack, not in a stack, checkout failure, custom
trunk branch name, and positional argument rejection
Modified files:
- cmd/root.go: register TrunkCmd in the "nav" command group
- README.md: add `gh stack trunk` to the Navigation section
- docs/src/content/docs/reference/cli.md: add `gh stack trunk`
reference section
* address review comments
* increment skill version
Sameen Karim