fix(assistant): move assistant button to menubar

[mejo-]

• Fixes: Floating Nextcloud Assistant icon is not visible if "full width editor" is enabled on Notes & Collectives #7453
• Fixes: Buttons outside editor (smart picker, assistent, link settings) invisible in mobile and embedded editors #7272
• Fixes: Assistant button is overlapping text #7817

Also removes superfluous extra translate button from menubar.

🖼️ Screenshots

🏚️ Before	🏡 After

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.96%. Comparing base (0bd9ce6) to head (9aa0a44).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/Menu/AssistantAction.vue	0.00%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #7883 +/- ##
==========================================
- Coverage 47.06% 45.96% -1.11% 
==========================================
Files 141 141 Lines 3886 3964 +78 Branches 733 747 +14 ==========================================
- Hits 1829 1822 -7 - Misses 1763 1838 +75 - Partials 294 304 +10 

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[mejo-]

/backport to stable32