[WIP] Add translation for mblock_clear_clipboard

[Copilot]

Fix missing translation for mblock_clear_clipboard

Issue: The translation key mblock_clear_clipboard is defined in all language files but not being replaced in the UI, showing as literal text {{mblock_clear_clipboard}} instead of the translated text.

Root Cause: The MBlockParser::replaceLanguagePlaceholders() method only handles translation placeholders with the pattern {{mblock::language_key}}, but the code uses the simpler pattern {{language_key}} (without the mblock:: prefix).

Solution: Update the replaceLanguagePlaceholders() method to also handle the simpler {{language_key}} pattern.

Progress Checklist:

• Explore repository structure and understand the codebase
• Identify the root cause of the missing translation
• Update MBlockParser to handle both translation placeholder patterns
• Test the fix to ensure translations work correctly
• Verify no other translations are broken

Original prompt

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This section details on the original issue you should resolve

<issue_title>Übersetzung fehlt: mblock_clear_clipboard</issue_title>
<issue_description>

MBlock: 4.3.5</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #212

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