HTS from Solidity — landing page (evm/hedera-services/hts-solidity/index)

**Page:** `evm/hedera-services/hts-solidity/index.mdx`

**Context:** Sibling `create-tokens.mdx` is written; this index plus `transfer-tokens`, `nft-operations`, `token-management` are placeholders.

**Scope:** Landing for managing HTS tokens from Solidity; introduce the `IHederaTokenService` interface and link the four operation pages.

### 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)