🎨 Palette: Add Loading States to Auth Forms

[singhaditya21]

💡 What: Added loading state logic (temporary text change and disabled=true) to the submit buttons on the Login and Registration forms. Implemented .btn:disabled CSS to reduce opacity and show a not-allowed cursor.
🎯 Why: Async network requests previously provided no immediate visual feedback, allowing users to rapidly click the submit button multiple times which could lead to duplicate API calls and a frustrating UX.
📸 Before/After: Before, buttons remained fully active and unchanged after clicking. Now, they visibly update to "Logging in..." or "Signing up..." and prevent further interaction until the request resolves.
♿ Accessibility: Ensures that screen readers and keyboard users receive feedback that their action is being processed and that the form is temporarily locked.

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PR created automatically by Jules for task 13229582785659442353 started by @singhaditya21

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