[PER-10667] Align public gallery date with detail view

[aasandei-vsp]

The public gallery card rendered its date from displayDT (mapped from the API's displayDate), while the detail sidebar reads displayTime || displayDT. For items where those fields diverge, the gallery showed a different date than the detail panel.

Base the public-archive date on the existing startDisplayTime getter (displayTime with EDTF interval-start handling, falling back to displayDT) so the gallery matches the sidebar's field preference. Add spec coverage for the displayTime, displayDT-fallback, and EDTF-interval cases.

Issue: PER-10667

The dates I have found as being inconsistent with the rest of the app was in the gallery, so I have changed it to displayTime/displayDT:

The dates in the public folder behave as expected, like in private or shared.
Also, we are not actually supporting a friendly timezone as of now, but we will once the EDTF date will be released.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.23%. Comparing base (17c0975) to head (4323cbd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1099      +/-   ##
==========================================
+ Coverage   52.15%   52.23%   +0.08%     
==========================================
  Files         354      354              
  Lines       12090    12090              
  Branches     2186     2186              
==========================================
+ Hits         6305     6315      +10     
+ Misses       5560     5549      -11     
- Partials      225      226       +1     

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