[ni1saux]

Adds a --dashboard-by option that chooses which breakdowns the dashboard shows. It applies to both the default HTML output and testdoc management.

testdoc --dashboard-by=tags,subdirectories tests/ TestDocumentation.html

Change

• --dashboard-by takes a comma-separated list of tags and/or subdirectories. Cards appear in the order given. The default is tags, so existing output is unchanged.
• New Tests per Subdirectory card. It lists every directory under the given path that contains tests, in tree order and indented by depth. Each count includes nested folders. Labels use the real folder names on disk (e.g. mp_b2b, not Robot's Mp B2b), and hovering a row shows the full path.
• Can also be set in TOML: dashboard_by = ["tags", "subdirectories"] (or "tags,subdirectories").
• Unknown values (e.g. tags,owners) fail with a clear --dashboard-by error.
• The tag card and the new card share the same bar-drawing code. Docs: new row in docs/cli/cli.md.

Testing

• New tests cover option parsing and validation, the TOML string or list forms, and the setting reaching the generated page.
• Checked against atest/testdata/performance/tests (nested counts, e.g. api 5008 → api/b2b 891) and against a real project.
• test_cli_management_generates_web_app_and_documentation, test_cli_cmd_mkdocs and test_cli_cmd_mkdocs_custom_template fail locally with FileNotFoundError. They fail the same way on main, apparently because the mkdocs executable isn't on PATH.