feat(help): route contextual command rows to shared explainers

[robkam]

Summary

Split Cross-Cutting Operator Semantics from Local Context Pages so contextual F1 pages stay local while shared operator semantics open through shared explainers.

• move repeated copy/move target and jump semantics into shared authored help topics and regenerate runtime/man assets
• wire contextual runtime help rows and footer hints around shared-topic follow, contents, and navigation behavior
• update focused help source/generator/runtime tests to validate the follow/back workflow instead of the old inline-detail model

Validation

• Red: source .venv/bin/activate && pytest -q tests/test_help_text_contract.py::test_split_file_help_arrows_follow_rows_without_wrapping tests/test_help_text_contract.py::test_main_f1_help_tracks_directory_file_preview_and_split_contexts
• make help-assets
• make clean && make
• source .venv/bin/activate && pytest -q tests/test_help_source_schema.py tests/test_help_generator.py tests/test_help_text_contract.py