Sustainability — landing page (solutions/sustainability/index)

[theekrystallee]

Page: solutions/sustainability/index.mdx

Context: Sibling guardian.mdx is written.

Scope: Overview of sustainability/ESG solutions; route into Guardian.

Acceptance criteria

• Replace the placeholder template with a real landing page
• Remove hidden: true from the frontmatter
• No "Browse by section" block — the side nav covers that; open straight into the deep-dive sections
• Route into the written sibling pages via <CardGroup>/<Card>
• Follow the style guide (markdown tables only; no AI-tell phrasing)