preact 03-routing: three views in one SPA

Hand-rolled useHashRoute hook (~10 lines) instead of preact-router —
hashchange listener + useState. Sidebar with Profile / Contacts /
Calendar, active state wired.

One typed data island per view (Person / AddressBook / Event) so each
view reads its own without a shared store. Read-only — inline edit is
stage 2's concern; stage 3 is about navigation shape.

Author: melvincarvalho