🎨 Palette: Add keyboard accessibility and focus states to custom interactive elements

[thirdeyenation]

💡 What: Added keyboard accessibility (tab index, roles, and keydown handlers) and visual focus states (:focus-visible) to several custom interactive elements that were previously only styled for mouse hover. This includes the welcome screen action cards, refresh/dismiss buttons, the chat input bottom actions menu (e.g., "Add attachments"), and the bottom action bar.

🎯 Why: Custom interactive elements (like div or label tags acting as buttons) were inaccessible to keyboard users. They lacked the ability to receive focus, trigger actions via the keyboard, and provide visual feedback when focused. This change ensures users navigating with a keyboard have a smooth and intuitive experience matching mouse users.

📸 Before/After:
(Before) Keyboard users could not tab to the "New Chat" or "Projects" cards on the welcome screen, nor could they trigger them with Enter/Space. Focus indicators were missing.
(After) Keyboard users can tab through all action cards and buttons, seeing a clear visual indicator (the same style as a mouse hover), and trigger them using standard keyboard interactions.

♿ Accessibility:

• Added role="button" and tabindex="0" to make custom elements focusable and semantically correct.
• Added @keydown.enter and @keydown.space.prevent to enable keyboard activation.
• Added :focus-visible to existing :hover CSS rules to provide clear visual focus indicators without showing ugly outlines on mouse clicks.

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PR created automatically by Jules for task 9076906869846407962 started by @thirdeyenation

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