fix: support DQ expectations without quarantine targets

[ravi-databricks]

Summary

• Allow Bronze and Silver DQ rules without requiring quarantine metadata.
• Preserve optional quarantine metadata when rules are absent.
• Warn when expect_or_quarantine has an incomplete target.
• Maintain compatibility with legacy onboarding files.
• Add JSON/YAML demo, unit, and integration coverage.
• Document quarantine behavior and limitations.

Validation

• FEVM backward compatibility test passed: v0.1.1 → current worktree.
• Added unit and integration assertions for both JSON and YAML configurations.
• Verified legacy quarantine-only configurations continue onboarding unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.24%. Comparing base (6cf7255) to head (b1fc569).
⚠️ Report is 6 commits behind head on v0.1.1.

Additional details and impacted files

@@            Coverage Diff             @@
##           v0.1.1     #487      +/-   ##
==========================================
+ Coverage   89.17%   89.24%   +0.06%     
==========================================
  Files          18       18              
  Lines        5009     5030      +21     
  Branches     1024     1029       +5     
==========================================
+ Hits         4467     4489      +22     
  Misses        313      313              
+ Partials      229      228       -1     

Flag	Coverage Δ
unittests	89.24% <100.00%> (+0.06%)	⬆️

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[brij-raghuwanshi-db]

Approved.