TREK 3.1 overhauls backend, adds passkey login, maps upgrade, and better expense splitting

TREK 3.1 introduces several major changes for users planning a travel with real-time collaboration, interactive maps, packing lists, and much more. The most substantial change is a complete backend migration from Express to NestJS, accompanied by a frontend upgrade to React 19; both segments now share a single Zod contract package, ensuring alignment between requests and responses. Alongside these architectural revisions, 18 vulnerabilities have been resolved, including a critical authentication bypass. Cost tracking has been redesigned into a Splitwise-style shared expense tracker crafted for group trips, providing an easier way to manage expenses. Security and accessibility are further improved: users may now register passkeys and log in with Face ID, Touch ID, or security keys. Building on core trip planning, two-way flight synchronization with AirTrail is now available. Day routes displayed on maps use real road networks with travel-time connectors, replacing straight-line estimate...