Write 'Hardhat Setup' (evm/tools/hardhat/setup)

**Page:** `evm/tools/hardhat/setup.mdx`

**Context:** Siblings `index`, `forking-basic`, `forking-advanced`, `testing` exist (`testing` also a placeholder). `evm/tools/foundry/setup` is a good structural model.

**Scope:** Configure Hardhat for Hedera from scratch — network config, `hardhat.config`, accounts, hashio/JSON-RPC endpoints.

### Acceptance criteria
- [ ] Replace the placeholder template with real content
- [ ] Remove `hidden: true` from the frontmatter
- [ ] Follow the style guide: **markdown tables only** (no HTML ``), and avoid AI-tell phrasing (no em-dashes, "delve", "leverage", "not just X but Y")
- [ ] Add working cross-links to related pages
- [ ] Confirm any code samples run on testnet