Remove unused isPending from RouterContext

[kentcdodds]

Fixes #27

Summary

• Stop passing isPending from useTransition into RouterContext across router and actions exercises
• Use const [, startTransition] = useTransition() since only startTransition is needed
• Update the pending-ui exercise README and learner comments to describe comparing location and nextLocation instead

Test plan

• Pending UI still works in exercises that compare location vs nextLocation (e.g. ship search, ship details)
• Navigation still uses startTransition for content updates

Made with Cursor

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Note

Low Risk
Low risk: removes an unused context value and adjusts useTransition destructuring without changing navigation or transition behavior.

Overview
Removes isPending from the RouterContext value across multiple router/actions exercises, since these modules only rely on startTransition and track pending UI via location vs nextLocation.

Updates each affected Root component to destructure useTransition() as const [, startTransition] = useTransition() and stops passing isPending through context.

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