Extend the node overview page showing deeper report

Problem/Motivation

The per-node audit page (/node/{nid}/content-first-audit) rendered by NodeAuditController shows only a flat count per check (e.g., "3" for empty blocks or "2" for missing alt attributes). This gives editors no actionable detail: they cannot tell which images are missing their alt attribute, nor which block-level tags are empty. The report is accurate but not useful enough to act on without manually inspecting the page.

Proposed resolution

• Empty block breakdown. Extend EmptyBlockTagCheck (and its storage/display layer) to return a per-tag breakdown rather than a single integer. For example, instead of "5", the report should show "3 <p>, 2 <div> are empty". The AuditFields format callable and the table row in NodeAuditController should be updated to render this structured detail.
• Affected images detail. For the missing_alt_count and empty_alt_count checks, capture the src (and, where present, the surrounding context such as a file name) of each offending <img>; element.
  Display these as an expandable list or a sub-row in the node audit table so editors can identify and fix the specific images.