feat(21-03): remove slide-out panels from root layout and clean UIStore

- Remove Item and Candidate SlideOutPanel instances from __root.tsx
- Remove SlideOutPanel, ItemForm, CandidateForm imports from root
- Remove panel state (panelMode, editingItemId, candidatePanelMode, editingCandidateId) from UIStore
- Remove panel actions (openEditPanel, openAddPanel, closePanel, etc.) from UIStore
- Preserve currentThreadId derivation for CandidateDeleteDialog
- Update CollectionView empty state to use catalog search instead of add panel
- Update ItemForm/CandidateForm with onClose prop replacing store panel close
- Clean all dead panel references across src/client/

src/client/routes/__root.tsx

@@ -9,14 +9,11 @@ import {
 } from "@tanstack/react-router";
 import { useState } from "react";
 import "../app.css";
-import { CandidateForm } from "../components/CandidateForm";
 import { CatalogSearchOverlay } from "../components/CatalogSearchOverlay";
 import { ConfirmDialog } from "../components/ConfirmDialog";
 import { ExternalLinkDialog } from "../components/ExternalLinkDialog";
 import { FabMenu } from "../components/FabMenu";
-import { ItemForm } from "../components/ItemForm";
 import { OnboardingWizard } from "../components/OnboardingWizard";
-import { SlideOutPanel } from "../components/SlideOutPanel";
 import { TotalsBar } from "../components/TotalsBar";
 import { useAuth } from "../hooks/useAuth";
 import { useDeleteCandidate } from "../hooks/useCandidates";
@@ -79,16 +76,6 @@ function RootLayout() {
 	const { data: auth, isLoading: authLoading } = useAuth();
 	const isAuthenticated = !!auth?.user;
 
-	// Item panel state
-	const panelMode = useUIStore((s) => s.panelMode);
-	const editingItemId = useUIStore((s) => s.editingItemId);
-	const closePanel = useUIStore((s) => s.closePanel);
-
-	// Candidate panel state
-	const candidatePanelMode = useUIStore((s) => s.candidatePanelMode);
-	const editingCandidateId = useUIStore((s) => s.editingCandidateId);
-	const closeCandidatePanel = useUIStore((s) => s.closeCandidatePanel);
-
 	// Candidate delete state
 	const confirmDeleteCandidateId = useUIStore(
 		(s) => s.confirmDeleteCandidateId,
@@ -114,9 +101,6 @@ function RootLayout() {
 		!wizardDismissed &&
 		isAuthenticated;
 
-	const isItemPanelOpen = panelMode !== "closed";
-	const isCandidatePanelOpen = candidatePanelMode !== "closed";
-
 	// Route matching for contextual behavior
 	const matchRoute = useMatchRoute();
 
@@ -186,40 +170,6 @@ function RootLayout() {
 			<TotalsBar {...finalTotalsProps} />
 			<Outlet />
 
-			{/* Item Slide-out Panel */}
-			<SlideOutPanel
-				isOpen={isItemPanelOpen}
-				onClose={closePanel}
-				title={panelMode === "add" ? "Add Item" : "Edit Item"}
-			>
-				{panelMode === "add" && <ItemForm mode="add" />}
-				{panelMode === "edit" && (
-					<ItemForm mode="edit" itemId={editingItemId} />
-				)}
-			</SlideOutPanel>
-
-			{/* Candidate Slide-out Panel */}
-			{currentThreadId != null && (
-				<SlideOutPanel
-					isOpen={isCandidatePanelOpen}
-					onClose={closeCandidatePanel}
-					title={
-						candidatePanelMode === "add" ? "Add Candidate" : "Edit Candidate"
-					}
-				>
-					{candidatePanelMode === "add" && (
-						<CandidateForm mode="add" threadId={currentThreadId} />
-					)}
-					{candidatePanelMode === "edit" && (
-						<CandidateForm
-							mode="edit"
-							threadId={currentThreadId}
-							candidateId={editingCandidateId}
-						/>
-					)}
-				</SlideOutPanel>
-			)}
-
 			{/* Item Confirm Delete Dialog */}
 			<ConfirmDialog />