enhance(logistics): add offline caching to qr code handoff generator (#152)

[QueenColly]

Closes #152

Summary of Work Done:
Implemented offline-first functionality for the QR Code Handoff Generator to ensure drivers can complete handoffs in zero-connectivity zones. The implementation strictly follows the Component -> Hook -> Service architectural pattern.

Implementation Details:

Service Layer (services/offlineStorageService.ts): Built a service using IndexedDB/localStorage to cache the handoff payload fetched from the live backend API (no mock objects used). Also added a queue mechanism to temporarily store successful scan confirmations.

Hook Layer (hooks/useOfflineQr.ts): Created a custom hook that attempts to fetch the live payload, falls back to the cached service data on network timeout, and listens for the window online event to sync queued scan confirmations back to the server.

Component Layer (components/logistics/QrGenerator.tsx): Refactored the UI to consume useOfflineQr. It seamlessly renders the qrcode.react component using the locally cached state when the device is entirely offline.

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