[codex] Add copy button for historical AI messages and add tooltip labels to message action buttons

[MyPyDavid]

Another vibe coded PR for the chatbot:

Motivation

• Ensure each AI message (including historical messages shown in chat history) has a small copy action button so users can copy assistant text from the conversation history.
• Provide localized tooltip text and aria-label attributes to match existing action buttons and improve accessibility.
• Add a German translation entry so the new tooltip is localizable.

Description

• Added Copy to clipboard tooltip lookup and helper functions (createCopyIcon, getMessageText, addCopyButton) to rdmo_chatbot/plugin/static/chatbot/js/copilot.js to build a copy icon, extract message text, and append a copy button that uses the Clipboard API with a textarea fallback.
• Updated the MutationObserver in rdmo_chatbot/plugin/static/chatbot/js/copilot.js to set title and aria-label for existing action buttons (Insert as answer, Contact support, and Copy to clipboard) and to call addCopyButton for each .ai-message in the copilot shadow DOM so historical AI messages receive the copy button.
• The copy button reuses the class of existing action buttons when present and stops click propagation to avoid interfering with other handlers.
• Added the German translation msgid "Copy to clipboard" / msgstr "In die Zwischenablage kopieren" to rdmo_chatbot/plugin/locale/de/LC_MESSAGES/djangojs.po.

Testing

• No automated tests were executed for these changes.

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Codex Task