🎨 Palette: Improve form accessibility and character limits

[Sczitzo]

💡 What: Added progressive color feedback (orange/red) to the alternative thought character counter and removed a redundant aria-describedby attribute on the automatic thought input.
🎯 Why: Enhances UX by visually warning users when they approach the character limit. Removing the redundant description prevents duplicate screen reader announcements.
📸 Before/After: Verified visually via Playwright isolated tests.
♿ Accessibility: Ensures the character limit warning is accessible without noisy screen reader updates on every keystroke by conditionally rendering sr-only static role="status" elements, and fixes duplicate announcement for optional text already nested in labels.

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PR created automatically by Jules for task 3263426987770494971 started by @Sczitzo

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