🎨 Palette: Enforce plain text on QTextEdit widgets

[dieterolson]

💡 What: Added setAcceptRichText(False) to QTextEdit widgets across the application (system prompt, chat history, download log, and setup log).
🎯 Why: By default, QTextEdit accepts rich text. If a user copies text from a webpage or a formatted document and pastes it into these fields, the text retains unwanted fonts, sizes, background colors, and styling. Disabling rich text acceptance ensures a clean, consistent plain text experience.
📸 Before/After: No visual changes directly, but prevents visual bugs caused by pasting formatted text.
♿ Accessibility: Prevents inconsistent text styling that could disrupt readability or contrast.

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PR created automatically by Jules for task 9452309341866597451 started by @dieterolson

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