fix: restore Sentrux workflow parsing and output handling

[AlexMikhalev]

Problem and change

GitHub rejects the Sentrux workflow before creating any job because multiline Markdown inside a shell assignment escaped the YAML run: | indentation. Indent those continuation lines, quote output-file/scalar expansions, and group the multiline report append. The Sentrux workflow remains manual-only with the same runner and permissions.

The existing hosted workflow-contract CI now checks this workflow and runs four real Bash tests for output files with spaces, complete multiline report preservation, baseline values and the degradation threshold. No Sentrux execution, remote comment posting or secret-bearing runner dispatch was performed.

Validation

• Full actionlint passes for both changed workflows, including ShellCheck, with no diagnostics.
• All seven extracted shell bodies pass bash -n.
• python3 -m unittest tests.workflow_sentrux_shell_test -v: four tests pass.
• UBS Python: zero critical/warning findings; YAML is unsupported by UBS and was checked by actionlint.

Closes #985. Gitea cross-link is pending restoration of the existing CLI/connector access; credentials were not changed.