Governance — landing page (solutions/governance/index)

**Page:** `solutions/governance/index.mdx`

**Context:** Subdir `hashiodao/` is fully written (proposals, token DAO, multisig, NFT DAO, setup).

**Scope:** Overview of on-chain governance on Hedera; route into HashioDAO.

### 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)