Add navigation progress bar

[kentcdodds]

Summary

• Add Kody-style router lifecycle events: navigationstart and navigationend for loader-backed navigation, form POST redirect chains, programmatic navigation, and instant hash/popstate paths.
• Add latest-wins abort semantics so superseded loader/form navigations do not emit stale completion events.
• Mount a root-level NavigationProgress component with spin-delay timing, trickle progress, minimum visible duration, and fade-out.
• Add E2E coverage that delays the chat route loader and verifies the progress bar appears and clears.

Walkthrough

Testing

• bun run typecheck
• bun run lint
• bun run test:unit
• bun run build
• bun tools/prepare-e2e-env.ts && bunx playwright test e2e/chat.spec.ts -g "navigation progress"
• bun run test:e2e
• Manual/headed browser walkthrough showing the top progress bar during delayed Chat route loading.