fix(paywall): replace hardcoded USDC label with dynamic token name

Read token name from firstRequirement.extra.name with a neutral
"Token" fallback instead of hardcoding "USDC". Aligns with #1926
which takes the same approach for the server-side fallback paywall.

Affected display strings: payment header, testnet prompt, balance
display, amount row, insufficient balance error message.

This PR was prepared with the assistance of a coding agent and
reviewed by Ryan R. Fox (an actual human) before submission.

Author: ryanRfox

go/http/evm_paywall_template.go

@@ -50,6 +50,7 @@ export function EvmPaywall({ paymentRequired, onSuccessfulResponse }: EvmPaywall
 
   const network = firstRequirement.network;
   const tokenAddress = firstRequirement.asset as `0x${string}`;
+  const tokenName = (firstRequirement.extra?.name as string) || "Token";
   const chainName = getNetworkDisplayName(network);
   const testnet = isTestnetNetwork(network);
 
@@ -145,7 +146,7 @@ export function EvmPaywall({ paymentRequired, onSuccessfulResponse }: EvmPaywall
       const balance = await getTokenBalance(publicClient, address, tokenAddress);
 
       if (balance === 0n) {
-        throw new Error(`Insufficient balance. Make sure you have USDC on ${chainName}`);
+        throw new Error(`Insufficient balance. Make sure you have ${tokenName} on ${chainName}`);
       }
 
       setStatus("Creating payment signature...");
@@ -199,11 +200,11 @@ export function EvmPaywall({ paymentRequired, onSuccessfulResponse }: EvmPaywall
         <h1 className="title">Payment Required</h1>
         <p>
           {paymentRequired.resource?.description && `${paymentRequired.resource.description}.`} To
-          access this content, please pay ${amount} {chainName} USDC.
+          access this content, please pay ${amount} {tokenName}.
         </p>
         {testnet && (
           <p className="instructions">
-            Need {chainName} USDC?{" "}
+            Need {tokenName} on {chainName}?{" "}
             <a href="https://faucet.circle.com/" target="_blank" rel="noopener noreferrer">
               Get some <u>here</u>.
             </a>
@@ -261,13 +262,17 @@ export function EvmPaywall({ paymentRequired, onSuccessfulResponse }: EvmPaywall
                 <span className="payment-label">Available balance:</span>
                 <span className="payment-value">
                   <button className="balance-button" onClick={() => setHideBalance(prev => !prev)}>
-                    {formattedBalance && !hideBalance ? `$${formattedBalance} USDC` : "••••• USDC"}
+                    {formattedBalance && !hideBalance
+                      ? `$${formattedBalance} ${tokenName}`
+                      : `••••• ${tokenName}`}
                   </button>
                 </span>
               </div>
               <div className="payment-row">
                 <span className="payment-label">Amount:</span>
-                <span className="payment-value">${amount} USDC</span>
+                <span className="payment-value">
+                  ${amount} {tokenName}
+                </span>
               </div>
               <div className="payment-row">
                 <span className="payment-label">Network:</span>