Remove mention of assistants and replace with AI apps

[haleychaas]

Updating mention of assistants and agents to be AI apps instead (agents are reserved for Agentforce).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.59%. Comparing base (b466937) to head (ad45d6f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2432   +/-   ##
=======================================
  Coverage   92.59%   92.59%           
=======================================
  Files          36       36           
  Lines        7472     7472           
  Branches      653      653           
=======================================
  Hits         6919     6919           
  Misses        545      545           
  Partials        8        8           

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