feat(cli): replace --verbose/--error with a single --log-level flag

[neurolabs]

Closes #16

[codecov]

Codecov Report

❌ Patch coverage is 98.48485% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.06%. Comparing base (6e754e9) to head (f5a4c1a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/opencode-sandbox/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #28      +/-   ##
==========================================
+ Coverage   87.93%   88.06%   +0.12%     
==========================================
  Files          86       86              
  Lines        5147     5186      +39     
==========================================
+ Hits         4526     4567      +41     
+ Misses        432      431       -1     
+ Partials      189      188       -1     

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