Help wanted: add table caption diagnostics

[zxyasfas]

User pain

Table caption requirements vary across thesis and journal formats. Users need actionable diagnostics for caption position, numbering, and style.

Expected PR

• Add one focused table-caption check or improve one existing message.
• Include a suggested fix in the diagnostic.
• Add a synthetic failing case.

Acceptance criteria

• format_report.json or format_report.html points users to the table-caption problem.
• Tests cover the new or changed behavior.
• Standard validation commands pass.

Privacy

Use synthetic table text and fake captions only.