feat: add wiki button to agenda list for hackathon sessions

[NGPixel]

• Adds a wiki button (blue book icon) in lieu of the notepad button for hackathon sessions (notepad being irrelevant and never used for them AFAIK). See below for example.
• Replaces the special arrow symbol on the "Switch to text-only version" button while the agenda is loading with a standard » symbol. Should fix the arrow sometimes changing to a weird icon because of incorrect font / charset / font not loaded.

[rjsparks]

I'm not sure on this one.
I think we should split the arrow font out into its own PR.
I'd like to talk about generalizing this to other sessions that have different things than the default notes location.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.73%. Comparing base (6b77807) to head (3ad2f29).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8133   +/-   ##
=======================================
  Coverage   88.72%   88.73%           
=======================================
  Files         310      310           
  Lines       40882    40882           
=======================================
+ Hits        36273    36276    +3     
+ Misses       4609     4606    -3     

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