Native Integrations — define scope + landing (native/integrations/index)

**Page:** `native/integrations/index.mdx`

**Context:** This directory has *only* the index — no siblings yet.

⚠️ **Scope decision needed:** is this a landing for existing tutorials (`native/tutorials/advanced/walletconnect-dapp`, `mcp-server-setup`, Solutions AI tab) or net-new integration pages? Resolve, then build the landing.

### 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 ``/``
- [ ] Follow the style guide (markdown tables only; no AI-tell phrasing)