chore: remove "Free" wording from UI banner and modal CTAs

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/modal/ErrorModal.tsx

@@ -42,7 +42,7 @@ export default function ErrorModal({
           target="_blank"
           rel="noreferrer"
         >
-          <span className="text-link-color underline">Sign up for free.</span>
+          <span className="text-link-color underline">Sign up.</span>
         </a>
       </span>
     </div>

frontend/src/components/modal/GlobalErrorModal.tsx

@@ -48,7 +48,7 @@ export default function GlobalErrorModal({
             target="_blank"
             rel="noopener noreferrer"
           >
-            Sign up for free.
+            Sign up.
           </a>
         </div>
       }

frontend/src/layout/Header.tsx

@@ -154,7 +154,7 @@ export default function Header() {
               rel="noopener noreferrer"
             >
               <div className="flex min-w-[25%] items-center gap-2 font-bold">
-                Upgrade your HELM experience - Free
+                Upgrade your HELM experience
                 <BsBoxArrowUpRight className="h-[14px] w-[14px]" />
               </div>
             </a>