Write 'Why Use Native Services?' (evm/hedera-services/why-use-native-services)

**Page:** `evm/hedera-services/why-use-native-services.mdx`

**Scope:** Cost/performance case for the HTS system contract vs pure ERC; when each wins. Pairs with `hybrid/hts-vs-erc`.

### 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