refactor(storage): centralize storage and cache keys into storage-keys module

[Vishal-770]

Description

Storage and cache key string literals (e.g. deskly::cache::attendance, deskly::cache::attendance_detail_${classId}, vite-ui-theme) are currently scattered across multiple files.

Tasks

• Create src/lib/storage-keys.ts defining a centralized STORAGE_KEYS constant object.
• Replace all hardcoded storage key strings across components and hooks with STORAGE_KEYS references.