🎨 Palette: Accessible Form Controls and File Dropzone

[Nawayisus]

This PR implements several micro-UX and accessibility improvements as the Palette persona.

💡 What:

• Form labels now correctly point to their associated inputs.
• The custom drag-and-drop file upload zone has been converted into an accessible button. It can be navigated to via the Tab key, visually highlights when focused, and can be triggered by pressing Enter or Space.
• The progress bar area now correctly broadcasts updates to screen readers.

🎯 Why:
Custom interactive areas like <div> dropzones are completely invisible to keyboard-only users and screen readers by default. By mapping proper ARIA roles, tabindex, and wiring up the existing visual highlight functions to the focus and blur events, we ensure all users can easily discover and use the primary action of the application without needing a mouse.

♿ Accessibility:

• Added for attributes to all form labels.
• Added tabindex="0", role="button", and aria-label to #dropZone.
• Mapped focus/blur to visual highlight functions.
• Wired up keydown event listener to trigger file input on Enter or Space while preventing default scroll behaviors.
• Added aria-live="polite" and aria-valuenow updates to #progressBar.

A critical learning regarding the manual wiring required for custom accessible dropzones has been logged to .Jules/palette.md.

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PR created automatically by Jules for task 15269096028294885989 started by @Nawayisus

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