Expand the integration document corpus with combined-feature samples

[davidnmbond]

Deferred from phase 8 step 8.2.2.

Scope:

• Add the remaining combined-feature corpus documents:
  • realistic business letter
  • multi-page report with tables and charts
  • contract with complex numbering and headers
  • mixed-content document with text, tables, images, and footnotes
• Generate Word reference baselines
• Add coverage in the visual regression suite

Acceptance criteria:

• All planned combined-feature documents are present in test-assets
• Reference PNGs exist for each page
• Visual regression coverage includes the new corpus items