fix: \WalletCard.vue\ GraphQL variables (#191)

Refactor address interpolation in fetchWalletData to use a proper
GraphQL variables object instead of embedding the address directly
in the query string template literal.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

landing/src/components/WalletCard.vue

@@ -21,8 +21,8 @@ async function fetchWalletData(addr: string) {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify({
-        query: `{
-          holders(address: "${addr.toLowerCase()}") {
+        query: `query WalletData($address: String!) {
+          holders(address: $address) {
             balance
             totalEthSpent
             totalTokensAcquired
@@ -31,6 +31,7 @@ async function fetchWalletData(addr: string) {
             items { currentPriceWei }
           }
         }`,
+        variables: { address: addr.toLowerCase() },
       }),
     });
     const json = await res.json();