Fix nil error in Analytics.last_month

[jvendetti]

Summary

• Replace unsafe chained hash access (analytics[ont][:"#{year_num}"][:"#{month_num}"]) with Hash#dig to prevent NoMethodError when analytics[ont] is nil
• Default to 0 views and log a debug-level message when analytics data is missing for an ontology
• Add class-level LOGGER constant for structured logging
• Fix some RuboCop warnings

Test plan

• Verify Analytics.last_month returns results without errors when all ontology data is present
• Verify no exception is raised when analytics[ont] is nil for some ontologies
• Confirm debug log message appears when analytics data is missing

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.48%. Comparing base (67f3b05) to head (b854d0b).

Files with missing lines	Patch %	Lines
lib/ontologies_api_client/analytics.rb	18.18%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   67.21%   66.48%   -0.73%     
==========================================
  Files          29       29              
  Lines         915      919       +4     
  Branches      172      174       +2     
==========================================
- Hits          615      611       -4     
- Misses        300      308       +8     

Flag	Coverage Δ
3.2	66.48% <18.18%> (-0.73%)	⬇️

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