Fix #176: Autosave and persistence for notes

[Manu95021]

This PR resolves issue #176, where users lose unsaved changes when refreshing the page or navigating to another section in the SaveBook application.
Changes Implemented:
Introduced autosave with debounce to persist note changes automatically.
Notes are now restored after page refresh or route change.
Added UI feedback to indicate save status (“Saving…” / “Saved”).
Improved state management to rely less on temporary in-memory state and more on persistent storage (localStorage and backend).
How to Test:
Edit or create a note.
Refresh the page → content should persist.
Navigate to a different route and return → content should persist.
Observe autosave feedback while typing.
Impact:
Prevents accidental loss of user data.
Improves reliability and user trust.
Lays groundwork for future offline support or further persistence enhancements.

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[Manu95021]

please review it and merge

[HarshYadav152]

@Manu95021
Do these changes

1. Remove package-lock.json from repo root.
2. Revert any changes make to README.md
3. Here you write everything else remain unchanged
   • by this you removed required code from Notes.js
   • You just have to make changes to file with your implementation but do not remove any code from it until & unless it is become redundant.

keep your branch is up to date with main.

[HarshYadav152]

@Manu95021 Do these changes

1. Move useEffect from the bottom of the code to inside functional component Notes()
2. Also noteContent is not defined

[HarshYadav152]

@Manu95021 Have you updated your branch with request changes.

[HarshYadav152]

@Manu95021
useEffect must be used inside a component.

[HarshYadav152]

Close as requested by assignee