🎨 Palette: Add password visibility toggle to login form

[shadowcoder8]

💡 What:
Added a password visibility toggle button to the admin login form (frontend/login.html). Clicking the button toggles the input type between password and text, and updates the icon.

🎯 Why:
Users often mistype passwords. Providing a way to view the entered password is a standard UX best practice that reduces frustration and login errors.

📸 Before/After:
Before: Password field only showed dots. No way to verify input.
After: A small eye icon is integrated into the right side of the password field. Clicking it reveals the password text and changes the icon to a slashed eye.

♿ Accessibility:
The toggle is a <button> with a base aria-label of "Show password". When toggled, the JavaScript (frontend/login.js) dynamically updates the aria-label to "Hide password", ensuring screen reader users are always aware of the button's current function and state. A new entry in .Jules/palette.md was also recorded reflecting this learning.

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PR created automatically by Jules for task 14239276051664833731 started by @shadowcoder8

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