🎨 Palette: Add loading states to authentication buttons

[singhaditya21]

What: Added visual loading states (changing text to "Loading..." and disabling the button) to all authentication forms (Login, Register, and Google Sign-In) during asynchronous API calls. Also added a new palette.md journal entry.

Why: To provide immediate visual feedback to users that their request is being processed. This prevents multiple clicks on the submit buttons and improves perceived performance and system status visibility.

Before/After:

• Before: Clicking "Sign In with Email", "Sign Up", or "Continue with Google" provided no visual feedback on the button itself while the network request was in flight.
• After: The clicked button immediately disables and changes its text to "Loading...", then gracefully restores its original state regardless of API success or failure using try/finally blocks.

Accessibility:

• Disabling the button during the request prevents duplicate submissions and conveys a busy state to screen readers.
• The use of try/finally ensures that buttons don't remain stuck in a disabled state if an error occurs, maintaining navigability.

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PR created automatically by Jules for task 10155714658533912287 started by @singhaditya21

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