🎨 Palette: Add async loading states for auth forms

[singhaditya21]

💡 What: Added loading states to the Login, Register, and Google Sign In buttons. When clicked, the button text changes to '⏳ Loading...', it becomes disabled, and an aria-busy="true" attribute is added. The state is guaranteed to be restored using try/finally blocks.
🎯 Why: To provide immediate visual feedback during simulated asynchronous API calls and prevent users from double-submitting authentication forms.
📸 Before/After: Before, the buttons had no visual feedback or disabled state during submission. After, they provide clear feedback and lock interaction until the process completes.
♿ Accessibility: Added aria-busy="true" to communicate the loading state to assistive technologies, and disabled="true" to ensure keyboard users cannot trigger multiple submissions.

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PR created automatically by Jules for task 11626954485311952742 started by @singhaditya21

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