chore: Enable dupl linter in golangci-lint config

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Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cv

.golangci.yml

@@ -17,6 +17,7 @@ linters:
     - gosec              # Security issues
 
     # Code quality
+    - dupl               # Duplicated code blocks
     - gochecknoinits     # Disallow init functions
     - canonicalheader    # HTTP header canonicalization
     - dupword            # Duplicate words (typos)