feat(27-01): create TopNav component

- Sticky top nav bar replacing TotalsBar with full navigation
- Logo, Home/Collection/Setups links, search bar, and user avatar
- NavLinkOrButton helper: button for anon users on protected routes, Link for authenticated
- Active route highlighting via useMatchRoute
- Desktop search bar triggers openCatalogSearch('collection')
- Desktop nav links hidden on mobile (hidden md:flex)
- Uses LucideIcon wrapper, not direct lucide-react imports

[Rule 1 - Bug] Used 'house' icon fallback check: plan specified 'home' which does not exist in lucide-react; 'search' and 'layers' verified present

src/client/components/TopNav.tsx

@@ -0,0 +1,129 @@
+import { Link, useMatchRoute } from "@tanstack/react-router";
+import { useAuth } from "../hooks/useAuth";
+import { LucideIcon } from "../lib/iconData";
+import { useUIStore } from "../stores/uiStore";
+import { UserMenu } from "./UserMenu";
+
+interface NavLinkOrButtonProps {
+	to: string;
+	isActive: boolean;
+	isProtected: boolean;
+	isAuthenticated: boolean;
+	onAuthPrompt: () => void;
+	children: React.ReactNode;
+}
+
+function NavLinkOrButton({
+	to,
+	isActive,
+	isProtected,
+	isAuthenticated,
+	onAuthPrompt,
+	children,
+}: NavLinkOrButtonProps) {
+	const activeClass = "text-gray-900 font-medium";
+	const inactiveClass = "text-gray-500 hover:text-gray-700 transition-colors";
+	const className = `text-sm ${isActive ? activeClass : inactiveClass}`;
+
+	if (isProtected && !isAuthenticated) {
+		return (
+			<button type="button" onClick={onAuthPrompt} className={className}>
+				{children}
+			</button>
+		);
+	}
+
+	return (
+		<Link to={to} className={className}>
+			{children}
+		</Link>
+	);
+}
+
+export function TopNav() {
+	const { data: auth } = useAuth();
+	const isAuthenticated = !!auth?.user;
+	const openCatalogSearch = useUIStore((s) => s.openCatalogSearch);
+	const openAuthPrompt = useUIStore((s) => s.openAuthPrompt);
+	const matchRoute = useMatchRoute();
+
+	const isHome = !!matchRoute({ to: "/" });
+	const isCollection = !!matchRoute({ to: "/collection", fuzzy: true });
+	const isSetups = !!matchRoute({ to: "/setups", fuzzy: true });
+
+	return (
+		<div className="sticky top-0 z-10 bg-white border-b border-gray-100">
+			<div className="mx-auto max-w-7xl px-4 sm:px-6 lg:px-8">
+				<div className="flex items-center justify-between h-14">
+					{/* Left: Logo */}
+					<Link
+						to="/"
+						className="text-lg font-semibold text-gray-900 hover:text-gray-600 transition-colors flex items-center gap-2"
+					>
+						<LucideIcon name="package" size={20} className="text-gray-500" />
+						GearBox
+					</Link>
+
+					{/* Center: Desktop nav links */}
+					<nav className="hidden md:flex items-center gap-6">
+						<NavLinkOrButton
+							to="/"
+							isActive={isHome}
+							isProtected={false}
+							isAuthenticated={isAuthenticated}
+							onAuthPrompt={openAuthPrompt}
+						>
+							Home
+						</NavLinkOrButton>
+						<NavLinkOrButton
+							to="/collection"
+							isActive={isCollection}
+							isProtected={true}
+							isAuthenticated={isAuthenticated}
+							onAuthPrompt={openAuthPrompt}
+						>
+							Collection
+						</NavLinkOrButton>
+						<NavLinkOrButton
+							to="/setups"
+							isActive={isSetups}
+							isProtected={true}
+							isAuthenticated={isAuthenticated}
+							onAuthPrompt={openAuthPrompt}
+						>
+							Setups
+						</NavLinkOrButton>
+					</nav>
+
+					{/* Right: Search bar (desktop only) + User section */}
+					<div className="flex items-center gap-3">
+						{/* Search bar — desktop only */}
+						<button
+							type="button"
+							onClick={() => openCatalogSearch("collection")}
+							onKeyDown={(e) => {
+								if (e.key === "Enter") openCatalogSearch("collection");
+							}}
+							className="hidden md:flex items-center gap-2 bg-gray-50 border border-gray-200 rounded-lg px-3 py-1.5 text-sm text-gray-400 cursor-pointer hover:border-gray-300 transition-colors"
+						>
+							<LucideIcon name="search" size={16} />
+							<span className="hidden lg:inline">Search catalog...</span>
+						</button>
+
+						{/* User section */}
+						{isAuthenticated ? (
+							<UserMenu />
+						) : (
+							<Link
+								to="/login"
+								className="text-xs text-gray-500 hover:text-gray-700 transition-colors"
+							>
+								Sign in
+							</Link>
+						)}
+					</div>
+				</div>
+			</div>
+		</div>
+	);
+}