Replaced alert with toast notifications in StockList

[JiyaAgrawal27]

📝 Description

• The issue mentioned that login, signup, watchlist add and remove used alert option.
• On testing, when I checked on the webiste demo, I found that the alert was technically present in Watchlist, but it was not visible.
• This PR replaces alert() with react-toastify toast notifications for a modern, non-blocking, and user-friendly experience.
• Kindly check the changes in your system since I dont have the access to the API Keys to login and check my watchlist.

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✅ Changes Made

• Updated src/components/StockList.jsx to use toast instead of alert().
• Installed react-toastify dependency.
• Updated package.json & package-lock.json to include the new dependency.

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Fixes #71

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[SrigadaAkshayKumar]

@JiyaAgrawal27 could you place a screenshot or a video that how it displays the notifications

[JiyaAgrawal27]

@SrigadaAkshayKumar I can only add and remove from the watchlist if I login, and I dont have the apikeys to login, can you help me out in this.

[SrigadaAkshayKumar]

what api keys you are addressing i am not able to understand your message