fix: let llm provider as optional

[CarlJi]

No description provided.

[netlify]

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Name	Link
🔨 Latest commit	54bf589
🔍 Latest deploy log	https://app.netlify.com/sites/reviewbot-x/deploys/67500a6d220ff70008541523

[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 23.66%. Comparing base (e361936) to head (54bf589).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
main.go	0.00%	5 Missing ⚠️
internal/linters/agent.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #490      +/-   ##
==========================================
- Coverage   23.71%   23.66%   -0.06%     
==========================================
  Files          36       36              
  Lines        4920     4923       +3     
==========================================
- Hits         1167     1165       -2     
- Misses       3613     3617       +4     
- Partials      140      141       +1     

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