docs: document executable JAR service descriptor merging

[bednar]

Summary

• Document that executable JAR packaging must merge META-INF/services files for the query API.
• Add the common NameResolver 'unix' error users may see when service descriptors are overwritten.
• Show the Maven Shade ServicesResourceTransformer fix.

Validation

• mvn -q -DskipTests package
• git diff --check

Related to #404.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.29%. Comparing base (0b9001f) to head (4d89da9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #406   +/-   ##
=======================================
  Coverage   88.29%   88.29%           
=======================================
  Files          21       21           
  Lines        1547     1547           
  Branches      280      280           
=======================================
  Hits         1366     1366           
  Misses         83       83           
  Partials       98       98           

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