[Component] Extract LoginModal into reusable component

Currently, both MoodMirror and CareerCrack use similar but separate login/signup modals. This creates duplicate code that makes maintenance harder.

Let's follow the DRY (Don't Repeat Yourself) principle and:

✅ Your Task:
Create a shared LoginModal.jsx component
(put it inside src/components/common/ or a similar shared folder)

Move the current logic (Firebase Auth, input fields, toggle password, etc.) into that shared component

Replace the old modals in both MoodMirror and CareerCrack with this new reusable one

🔥 Important Notes:
Firebase Auth will still work in the new component
Just import it from your existing firebase.js setup:

js
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import { auth } from '../../firebase';
Feel free to pass props if each app needs minor changes
(e.g. title="Welcome to MoodMirror")

🏁 Result:
Cleaner, reusable code that’s easier to update and extend for future features like OAuth or validation!