feat: label the blackbeard extension by name

The Quantus browser wallet now injects itself as `blackbeard` instead of
`polkadot-js` (quantus/extension#15), so it no longer collides with the real
polkadot{.js} extension. qapi already found it by enumeration; this gives it
a label in the extension list instead of the raw key.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uDUodEcRbBwNRi3UCmw8f

src/pages/Accounts/AccountList.tsx

@@ -95,6 +95,7 @@ const AccountCard: FC<{
   )
 }
 export const knownExtensions: Record<string, string> = {
+  blackbeard: "blackbeard",
   "polkadot-js": "Polkadot JS",
   "nova-wallet": "Nova Wallet",
   talisman: "Talisman",