Add Markdown report section snapshots

[JuanTorchia]

Summary

• Add focused Markdown section snapshot assertions for representative report categories.
• Cover build, framework, language/source, concurrency/source, automation, and baseline sections.
• Assert stable section ordering without introducing external snapshot tooling.

Validation

• mvn clean test '-Dmaven.compiler.release=22' passes with 51 tests.

Closes #14