Tidy up "frontend"

[AlanGriffiths]

If we were to need a generic frontend we would need to rework stuff anyway. So no need to keep the last bit separate

[codecov]

Codecov Report

Merging #3061 (91589a6) into main (85bc5b0) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #3061   +/-   ##
=======================================
  Coverage   77.69%   77.69%           
=======================================
  Files        1056     1056           
  Lines       73409    73409           
=======================================
+ Hits        57037    57038    +1     
+ Misses      16372    16371    -1     

Files	Coverage Δ
...rc/server/frontend_wayland/session_credentials.cpp	45.45% <ø> (ø)

... and 2 files with indirect coverage changes

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[mattkae]

Not sure if the CI break is on your end, but the project builds and makes sense to me 👍