[DataEntry, TreeView] WIP: Improve narrow window UX

[imnasnainaec]

Based on #3787 (see diff: grid2...tree-view-sm)

Resolves #3812
Resolves #3813

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.92%. Comparing base (5b0ef75) to head (a36b943).
Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
Backend/Models/SemanticDomain.cs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3808      +/-   ##
==========================================
+ Coverage   72.90%   81.92%   +9.02%     
==========================================
  Files         286       51     -235     
  Lines       10739     4737    -6002     
  Branches     1335      588     -747     
==========================================
- Hits         7829     3881    -3948     
+ Misses       2512      700    -1812     
+ Partials      398      156     -242     

Flag	Coverage Δ
backend	81.92% <75.00%> (ø)
frontend	?

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[imnasnainaec]

Split into #3816 & #3847