🎨 Palette: Add accessibility attributes and focus rings to Navbar

[belpythons]

💡 What

Added crucial ARIA attributes (aria-expanded, aria-haspopup, aria-label) to disclosure widgets and icon-only interactive elements in the Navbar, along with explicit keyboard focus rings (focus-visible:ring-2).

🎯 Why

Icon-only buttons and disclosure widgets (like dropdowns and mobile menus) lacked implicit state communication to screen readers and clear visual feedback for keyboard users navigating via Tab.

📸 Before/After

• Before: Mobile menu toggle and theme toggle buttons only had hover states, with no clear indication of focus when tabbing. Screen readers couldn't identify if menus were open or closed.
• After: All interactive elements now feature a clear ring-accent-500 outline upon keyboard focus, and screen readers will announce the expanded/collapsed state of menus.

♿ Accessibility

• Added aria-expanded and aria-haspopup to the Forum dropdown.
• Added dynamic aria-label (Open/Close menu) and aria-expanded to the mobile menu toggle button.
• Applied focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-accent-500 to all icon-only buttons for high-visibility keyboard navigation.

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PR created automatically by Jules for task 3976537212447928048 started by @belpythons

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