🎨 Palette: Form and Dropzone Accessibility Improvements

[Nawayisus]

🎨 Palette: Accessibility improvements for form controls and upload dropzone

💡 What:
This PR implements several key accessibility improvements:

1. Form Labels: Explicitly linked all form labels (Original Language, Target Language, Output Format, Translation Provider) to their respective <select> inputs using the for attribute.
2. Upload Dropzone: Transformed the visual #dropZone div into a proper interactive element. Added tabindex="0" and role="button" so it receives keyboard focus. Implemented JavaScript logic to allow triggering the file upload via the Enter or Space keys, carefully ensuring that explicit clicks on the nested button or hidden input do not cause double-firing.
3. Progress Indicators: Added required ARIA attributes (aria-valuemin, aria-valuemax, aria-valuenow) to the progress bar and dynamically synchronized them in JS. Added aria-live="polite" to the progress area so screen readers announce status updates.
4. UX Documentation: Recorded a critical UX learning in .Jules/palette.md regarding the specific pattern of custom dropzones with nested explicit controls.

🎯 Why:
Previously, users relying on screen readers or keyboard navigation could not effectively interact with the file upload dropzone or understand the context of the dropdown menus. Furthermore, progress updates during translation were visually apparent but invisible to assistive technologies. These changes ensure the core functionality of the application is accessible to all users.

♿ Accessibility:

• Improved screen reader context for form inputs (for attributes).
• Restored keyboard accessibility for the primary call-to-action (file dropzone).
• Enabled dynamic status announcements (aria-live, aria-valuenow).

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PR created automatically by Jules for task 17692893474614019666 started by @Nawayisus

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