chore: standardize golangci-lint v2 setup

[tekenstam]

Summary

Closes #137

Standardizes the golangci-lint setup to the keikoproj standard:

• Add .golangci.yml with golangci-lint v2 config format (exclusion presets for common false positives, generated code, legacy patterns)
• Pin golangci-lint from latest → v2.11.4 in lint.yml for reproducible CI
• Bump GOLANGCI_LINT_VERSION in Makefile from v2.1.1 → v2.11.4 to keep in sync

Gosec security scan and license check jobs are unchanged.

Test plan

• Verify the golangci-lint CI check passes on this PR
• Confirm gosec and license check jobs continue to pass

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.37%. Comparing base (1655722) to head (817395d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #138   +/-   ##
=======================================
  Coverage   58.37%   58.37%           
=======================================
  Files          12       12           
  Lines         603      603           
=======================================
  Hits          352      352           
  Misses        232      232           
  Partials       19       19           

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