feat(config): add site_url config option

[qwqcode]

Add an ATK_SITE_URL environment variable and configuration option to allow modification of the default site URL, optimizing the deployment process experience.

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 31.29%. Comparing base (d2225d5) to head (4c734b7).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/core/conf_sync.go	25.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #967      +/-   ##
==========================================
- Coverage   31.40%   31.29%   -0.11%     
==========================================
  Files         205      205              
  Lines        8776     8780       +4     
==========================================
- Hits         2756     2748       -8     
- Misses       5868     5877       +9     
- Partials      152      155       +3     

Flag	Coverage Δ
go	31.29% <40.00%> (-0.11%)	⬇️

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