fix(upload-api): make text color explicit

set text color for body text on storacha branded email validation page to black, rather than relying on browser default color

upload-api/html-storacha/index.jsx

@@ -36,6 +36,7 @@ export function buildDocument(body) {
     }
 
     body {
+      color: black
       background-color: var(--hot-red-light);
       font-family: 'Epilogue', sans-serif;
       max-width: 70rem;