refactor: modify date, startTime and endTime format

for now date, startTime and endTime are stored as string, which i believe isn't good for long term, and validation pipeline is also setup on backend as string.
I want to refactor such that it will be stored in the normal form and while retrieving on client side only moment will format it. It will help to customize the date/time format on future if needed.
Thank you.

The payload does not name files, tests, models, or entry points. Start by searching the TypeScript repository for date, startTime, and endTime, then trace their database, backend validation, and client formatting paths. Confirm the intended stored types and coverage needed; done means all three fields use the normal storage form while the client controls display formatting.

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