Move dashboard update PR orchestration to Python

[danielporterda]

Summary

• Moves the existing version-dashboard update PR orchestration out of workflow bash and into a Python script, preserving dashboard-only behavior.

Stack

This is PR 7/8 in the generated-reference automation split.

Base: generated-reference-06-version-change-summary
Head: generated-reference-07-dashboard-pr-orchestrator

Validation

• python3 -m pytest tests/test_update_generated_reference_prs.py 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 scripts/update_generated_reference_prs.py --help; workflow YAML parse; git diff --check