Update Alchemy entry on Indexers page — Stellar Data API is now live

The entry described Alchemy as "in talks to expand to Stellar, targeted H1
2026." Alchemy's Stellar Data API has launched, so this updates the entry to
the actual offering (indexed transfer history, account balances, and NFT
holdings across native, Classic, and Soroban assets) with links to Alchemy's
Data API overview and JSON-RPC quickstart.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: mmazco

docs/data/indexers/README.mdx

@@ -27,7 +27,7 @@ Lots of apps need this kind of data, and it tends to have a standard shape. This
 
 In the biz, these are called _Portfolio APIs._ Well-known companies offering them:
 
-- [Alchemy]: most popular choice on Ethereum; now in talks to expand their service to Stellar, with a targeted launch in the first half of 2026.
+- [Alchemy]: a widely-used data provider (popular on Ethereum), now live on Stellar. Its [Stellar Data API](https://www.alchemy.com/docs/reference/stellar-data-api-overview) serves indexed **transfer history**, **account balances**, and **NFT holdings** across native, Stellar Classic, and Soroban assets — letting you query this data without running your own indexer (JSON request bodies, opaque `pageKey` pagination). Alchemy also provides [Stellar JSON-RPC](https://www.alchemy.com/docs/reference/stellar-api-quickstart) and appears in the [RPC providers](../apis/rpc/providers.mdx) list.
 
 - [Allium]: currently building Stellar support, launching Q1 2026