Give Constraints Summary cards a readable generated-index description

[rmcdaniel]

Problem

The generated Constraints category pages use the first content block from the Constraints Summary page as the card description. Because that page begins with a table, the card displays raw table syntax (| Constraint | Workflow code | Activity code |) instead of explaining what the page contains.

This affects both the stable 1.x category at /docs/category/constraints/ and the explicit 2.0 prerelease category at /docs/2.0/category/constraints/. The surrounding cards have readable summaries, so the Constraints Summary entry is uniquely opaque to a first-time reader on desktop and mobile.

Acceptance criteria

• Give the Constraints Summary page in both documentation versions a concise, human-readable description that the generated category card consumes.
• Preserve the stable 1.x default route, the explicit 2.0 route, sidebar order, and card links.
• Validate the two generated category pages at desktop, intermediate, and mobile widths; the Constraints Summary card must not expose Markdown table syntax.
• Avoid tests that pin ordinary prose, headings, or Markdown layout.

Delete when

Delete when both generated Constraints category pages show a readable Constraints Summary card description and the cards still navigate to the correct versioned pages.