chore: alias set() onto KaiselNavigator for symmetry with KaiselRouter

KaiselRouter.set(...) and KaiselNavigator.restoreStack(...) do the same thing under different names.

From context.shell().current you only get a KaiselNavigator, so code that deliberately assigns a branchs stack reads as state restoration:

// "pop this tab back to its root" when the active tab is tapped again
shell.current.restoreStack([DashboardTabRoute(item)]);

versus the equivalent at the root:

router.set([SomeRoute()]);

restoreStack is the right name for its other caller (state restoration), but at a deliberate-assignment call site it misleads — a reviewer reasonably asks what is being restored.

Suggestion

Add set to KaiselNavigator as an alias for restoreStack, or rename for symmetry and keep the old name deprecated for a release. Small, but it is on the path anyone building a branched shell with "tap active tab to reset" behaviour will walk.

Start by reading KaiselNavigator.restoreStack and comparing it with KaiselRouter.set, then trace how shell.current exposes the navigator. Confirm the preferred compatibility approach from the issue's alias-or-deprecation options. Done means deliberate stack assignment through KaiselNavigator has a symmetric set entry point while existing restoreStack behavior remains usable.