fix(cms): persist undo/redo history in sessionStorage

[AugistineCreates]

This pr closes #778

Overview:
This PR resolves an issue where the cmsStore undo/redo history was completely lost upon a page refresh within a single session. By introducing the Zustand persist middleware configured with sessionStorage, the history stack now gracefully survives page reloads. This ensures content editors don't lose their ability to undo mistakes after a browser crash or an accidental refresh.

Changes:

• Added Zustand persist middleware: Wrapped useCMSStore with persist to save the store state.
• sessionStorage Integration: Configured the storage to use sessionStorage so history is available after page refreshes but properly cleared when the browser tab closes.
• State Selection: Persisted the course, history, and historyIndex properties via the partialize option.
• Quota Optimization: Lowered the history limit from 50 to 20 items within setCourse and updateCourse to ensure the stored string length remains well within typical sessionStorage quota limits.
• Tests Coverage Added: Implemented src/store/cmsStore.test.ts to simulate and assert:
  • Correct persistence of state to sessionStorage.
  • Proper store rehydration, allowing undo functionality after a page refresh.
  • Verification that the history length never exceeds the 20 item limit.

Impacted Files:

• src/store/cmsStore.ts
• src/store/cmsStore.test.ts

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