Add generated update version summaries

[danielporterda]

Summary

• Adds a small utility that summarizes version changes for dashboard and source-config generated PR bodies.

Stack

This is PR 6/8 in the generated-reference automation split.

Base: generated-reference-05-wallet-source-updater
Head: generated-reference-06-version-change-summary

Validation

• python3 -m pytest tests/test_summarize_version_changes.py tests/test_update_generated_reference_sources.py tests/test_generate_network_component_versions.py tests/test_wallet_kernel_nav.py tests/test_docs_env.py; python3 -m py_compile scripts/summarize_version_changes.py; git diff --check