[REFACTOR] Centralize standard static strings into a constants file

[Aditya948351]

Hardcoded strings (like error messages and standard alerts) are scattered across components. Create a src/lib/constants.ts file and extract these strings into an exported object for cleaner maintenance.

[nishupr]

Hi @Aditya948351, I'd like to work on this issue. I'll create a src/lib/constants.ts file and extract the scattered hardcoded strings (error messages, alerts, etc.) into an exported object. Please assign this to me.

[github-actions]

Hi @nishupr! We have officially assigned this issue to you. Please start working on it, and good luck with your PR!

ETA: 3 days
Issue will be assigned to another contributor if failed to do so!

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