🎨 Palette: Add loading state and disable login/register buttons

[singhaditya21]

💡 What: Added disabled states and loading text ("⏳ Logging in..." / "⏳ Signing up...") to the login and register submit buttons during asynchronous authentication requests. The state is cleanly restored in a finally block to ensure robustness.
🎯 Why: When users perform asynchronous actions, lack of immediate visual feedback can lead to confusion and double-clicking, causing duplicate requests or errors. This change prevents duplicate submissions and gives users confidence that their request is being processed.
📸 Before/After:

• Before: Clicking login/register showed a toast but the button remained active.
• After: Clicking the button immediately disables it and changes its text to indicate a loading state, reverting only when the request completes.
  ♿ Accessibility: Prevents confusing focus/state management issues caused by double-submissions. Helps screen readers understand that an action has been triggered and is in progress.

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PR created automatically by Jules for task 9013498743607235571 started by @singhaditya21

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