feat(22-01): add UIStore modal states, AddToCollectionModal, and sonner toasts

- Extend UIStore with addToCollectionModal, addToThreadModal, catalogSessionThreadId
- Create AddToCollectionModal with category dropdown, notes, purchase price
- Install sonner and add Toaster + AddToCollectionModal to root layout
- closeCatalogSearch now resets catalogSessionThreadId

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/routes/__root.tsx

@@ -8,7 +8,9 @@ import {
 	useRouter,
 } from "@tanstack/react-router";
 import { useState } from "react";
+import { Toaster } from "sonner";
 import "../app.css";
+import { AddToCollectionModal } from "../components/AddToCollectionModal";
 import { CatalogSearchOverlay } from "../components/CatalogSearchOverlay";
 import { ConfirmDialog } from "../components/ConfirmDialog";
 import { ExternalLinkDialog } from "../components/ExternalLinkDialog";
@@ -204,6 +206,10 @@ function RootLayout() {
 			{/* Catalog Search Overlay */}
 			<CatalogSearchOverlay />
 
+			{/* Add to Collection Modal */}
+			<AddToCollectionModal />
+			<Toaster position="bottom-right" richColors />
+
 			{/* Onboarding Wizard */}
 			{showWizard && (
 				<OnboardingWizard onComplete={() => setWizardDismissed(true)} />