fix(ui/sidebar): show env variables in sidebar settings ui (#946)

[qwqcode]

This PR updates the artalk settings interface to display configuration values set via environment variables with a "Controlled by environment variables; cannot be modified" message. Since environment variables take priority over configuration files, the graphical interface will prevent changes to these variables. The interface will only allow modifications to configuration file settings, keeping environment variable settings read-only and consistent.

More details here.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 31.55%. Comparing base (587523f) to head (c56bbc7).
Report is 6 commits behind head on master.

Files	Patch %	Lines
server/handler/setting_get.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #956      +/-   ##
==========================================
- Coverage   31.63%   31.55%   -0.09%     
==========================================
  Files         204      204              
  Lines        8690     8694       +4     
==========================================
- Hits         2749     2743       -6     
- Misses       5790     5798       +8     
- Partials      151      153       +2     

Flag	Coverage Δ
go	31.55% <0.00%> (-0.09%)	⬇️

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