feat(web): /fields two-pane screen (grouped list + create form) + nav (no stubs left)

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

web/src/shell/app-shell.tsx

@@ -5,8 +5,6 @@ import { useLogout } from "../api/queries";
 import { Button } from "@/components/ui/button";
 import { LangSwitch } from "./lang-switch";
 
-const DISABLED_NAV = ["fields"] as const;
-
 export function AppShell() {
   const { t } = useTranslation();
   const navigate = useNavigate();
@@ -54,16 +52,14 @@ export function AppShell() {
           >
             {t("nav.search")}
           </NavLink>
-          {DISABLED_NAV.map((key) => (
-            <button
-              key={key}
-              disabled
-              title={t("nav.soon")}
-              className="block w-full cursor-not-allowed rounded px-2 py-1 text-left text-neutral-400"
-            >
-              {t(`nav.${key}`)}
-            </button>
-          ))}
+          <NavLink
+            to="/fields"
+            className={({ isActive }) =>
+              `block rounded px-2 py-1 ${isActive ? "bg-neutral-200 font-medium" : ""}`
+            }
+          >
+            {t("nav.fields")}
+          </NavLink>
         </nav>
       </aside>
       <div className="flex flex-1 flex-col">