feat(24-02): render-first root layout, guarded write actions, public setup viewing

- Remove authLoading spinner gate — app renders immediately for all visitors
- Expand isPublicRoute to include /, /global-items/*, /setups/*, /users/, /login
- Replace hard window.location.href redirect with soft navigate() after auth resolves
- Remove onboarding loading spinner — pass isAuthenticated as enabled to guard query
- Add AuthPromptModal to root JSX for global availability
- Guard Add to Collection and Add to Thread buttons with isAuthenticated check
- Rework setup detail page to use usePublicSetup for anonymous visitors
- Wrap all write action UI (Add Items, Delete, Public toggle, remove/classify) in isAuthenticated guards

src/client/routes/global-items/$globalItemId.tsx

@@ -1,4 +1,5 @@
 import { createFileRoute, Link } from "@tanstack/react-router";
+import { useAuth } from "../../hooks/useAuth";
 import { useFormatters } from "../../hooks/useFormatters";
 import { useGlobalItem } from "../../hooks/useGlobalItems";
 import { useUIStore } from "../../stores/uiStore";
@@ -11,8 +12,11 @@ function GlobalItemDetail() {
 	const { globalItemId } = Route.useParams();
 	const { data: item, isLoading, error } = useGlobalItem(Number(globalItemId));
 	const { weight, price } = useFormatters();
+	const { data: auth } = useAuth();
+	const isAuthenticated = !!auth?.user;
 	const openAddToCollection = useUIStore((s) => s.openAddToCollection);
 	const openAddToThread = useUIStore((s) => s.openAddToThread);
+	const openAuthPrompt = useUIStore((s) => s.openAuthPrompt);
 
 	if (isLoading) {
 		return (
@@ -133,18 +137,26 @@ function GlobalItemDetail() {
 			<div className="flex gap-3 mb-6">
 				<button
 					type="button"
-					onClick={() =>
-						openAddToCollection(item.id, `${item.brand} ${item.model}`)
-					}
+					onClick={() => {
+						if (!isAuthenticated) {
+							openAuthPrompt();
+							return;
+						}
+						openAddToCollection(item.id, `${item.brand} ${item.model}`);
+					}}
 					className="bg-gray-700 text-white rounded-lg px-5 py-2.5 text-sm font-medium hover:bg-gray-800 transition-colors"
 				>
 					Add to Collection
 				</button>
 				<button
 					type="button"
-					onClick={() =>
-						openAddToThread(item.id, `${item.brand} ${item.model}`)
-					}
+					onClick={() => {
+						if (!isAuthenticated) {
+							openAuthPrompt();
+							return;
+						}
+						openAddToThread(item.id, `${item.brand} ${item.model}`);
+					}}
 					className="bg-white text-gray-700 border border-gray-200 rounded-lg px-5 py-2.5 text-sm font-medium hover:bg-gray-50 transition-colors"
 				>
 					Add to Thread