allow multiple labels setting for breadcrum

[masao]

Summary

Support both a single property and a list of properties in the breadcrumb label configuration.

When multiple label properties are configured, ttl2html now checks them in order and uses the first property that has a value. If none of the configured properties match, it falls back to the default title generated by get_title.

This keeps the existing behavior for a single label property while allowing projects to define prioritized fallback properties for breadcrumb labels.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation or other updates (if none of the other choices apply)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Apply label fallback list to the current breadcrumb

This routes only parent breadcrumbs through the new fallback-list helper; the active/current item is still built in build_breadcrumbs with the old scalar lookup (data[@config[:breadcrumbs].first["label"]]), so when label is an array that lookup misses and a page such as ex:sect1 renders the default title Section 1 instead of the configured fallback Sect1. Please use the same fallback helper for the depth-0 label so the new option applies to every breadcrumb item.

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