fix(sentrix): testnet explorer URL + EIP3091 compliance

[satyakwok]

Small follow-up to #2707 — fixes the testnet (chain ID 7120) explorer entry.

What changed

   "explorers": [
     {
       "name": "Sentrix Scan (Testnet)",
-      "url": "https://scan.sentrixchain.com",
-      "standard": "none"
+      "url": "https://scan-testnet.sentrixchain.com",
+      "standard": "EIP3091"
     }
   ]

Why

1. URL was pointing to the mainnet host.

Sentrix Scan uses a two-host pattern (Etherscan-style):

• scan.sentrixchain.com — mainnet-locked
• scan-testnet.sentrixchain.com — testnet-locked

Host detection happens server-side; cookie-based toggle only flips the in-page UI. With the original scan.sentrixchain.com URL, a wallet deep-linking a testnet tx hash via chainlist would land on the mainnet host, query the mainnet API, and render "transaction not found".

The corrected URL scan-testnet.sentrixchain.com host-pins the request to testnet → wallet deep-links resolve correctly with zero user toggle.

2. Standard upgraded "none" → "EIP3091".

Same Next.js codebase serves both hosts. EIP-3091 paths verified live on the testnet host:

Path	Status
/block/<n>	200
/tx/<hash>	200
/address/<addr>	200
/token/<addr>	200

Verification

$ curl -s -o /dev/null -w "%{http_code}\n" https://scan-testnet.sentrixchain.com/block/2607000
200
$ curl -s -o /dev/null -w "%{http_code}\n" https://scan-testnet.sentrixchain.com/tx/0xabc
200
$ curl -s -o /dev/null -w "%{http_code}\n" https://scan-testnet.sentrixchain.com/address/0x682126f5f973bddda2c92fb0dfce8a4ba275c99b
200
$ curl -s -o /dev/null -w "%{http_code}\n" https://scan-testnet.sentrixchain.com/token/0xabc
200

Mainnet entry (chain ID 7119) untouched — already correct.