Add nested module discovery coverage

[Will-thom]

Summary

• add a nested Maven module fixture rooted at platform/service-core
• verify recursive module discovery includes root, parent, and nested module paths
• verify Surefire report mapping and reproduce command use the nested module path

Validation

• go test ./...
• go run ./cmd/prmaven fails -project pkg/prmaven/testdata/nested-module-project

Closes #6

[github-actions]

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