Extract useSidePanelState hook from App.tsx

Move panel view state, fold/pin state, isWideDesktop media query,
and all related handlers into a dedicated hook, reducing App.tsx
by ~80 lines of state management boilerplate.

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

apps/web/src/hooks/use-side-panel-state.ts

@@ -0,0 +1,101 @@
+import type { CreatureId } from "@initiative/domain";
+import { useCallback, useEffect, useState } from "react";
+
+type PanelView =
+	| { mode: "closed" }
+	| { mode: "creature"; creatureId: CreatureId }
+	| { mode: "bulk-import" }
+	| { mode: "source-manager" };
+
+interface SidePanelState {
+	panelView: PanelView;
+	selectedCreatureId: CreatureId | null;
+	bulkImportMode: boolean;
+	sourceManagerMode: boolean;
+	isRightPanelFolded: boolean;
+	pinnedCreatureId: CreatureId | null;
+	isWideDesktop: boolean;
+}
+
+interface SidePanelActions {
+	showCreature: (creatureId: CreatureId) => void;
+	showBulkImport: () => void;
+	showSourceManager: () => void;
+	dismissPanel: () => void;
+	toggleFold: () => void;
+	togglePin: () => void;
+	unpin: () => void;
+}
+
+export function useSidePanelState(): SidePanelState & SidePanelActions {
+	const [panelView, setPanelView] = useState<PanelView>({ mode: "closed" });
+	const [isRightPanelFolded, setIsRightPanelFolded] = useState(false);
+	const [pinnedCreatureId, setPinnedCreatureId] = useState<CreatureId | null>(
+		null,
+	);
+	const [isWideDesktop, setIsWideDesktop] = useState(
+		() => window.matchMedia("(min-width: 1280px)").matches,
+	);
+
+	useEffect(() => {
+		const mq = window.matchMedia("(min-width: 1280px)");
+		const handler = (e: MediaQueryListEvent) => setIsWideDesktop(e.matches);
+		mq.addEventListener("change", handler);
+		return () => mq.removeEventListener("change", handler);
+	}, []);
+
+	const selectedCreatureId =
+		panelView.mode === "creature" ? panelView.creatureId : null;
+
+	const showCreature = useCallback((creatureId: CreatureId) => {
+		setPanelView({ mode: "creature", creatureId });
+		setIsRightPanelFolded(false);
+	}, []);
+
+	const showBulkImport = useCallback(() => {
+		setPanelView({ mode: "bulk-import" });
+		setIsRightPanelFolded(false);
+	}, []);
+
+	const showSourceManager = useCallback(() => {
+		setPanelView({ mode: "source-manager" });
+		setIsRightPanelFolded(false);
+	}, []);
+
+	const dismissPanel = useCallback(() => {
+		setPanelView({ mode: "closed" });
+	}, []);
+
+	const toggleFold = useCallback(() => {
+		setIsRightPanelFolded((f) => !f);
+	}, []);
+
+	const togglePin = useCallback(() => {
+		if (selectedCreatureId) {
+			setPinnedCreatureId((prev) =>
+				prev === selectedCreatureId ? null : selectedCreatureId,
+			);
+		}
+	}, [selectedCreatureId]);
+
+	const unpin = useCallback(() => {
+		setPinnedCreatureId(null);
+	}, []);
+
+	return {
+		panelView,
+		selectedCreatureId,
+		bulkImportMode: panelView.mode === "bulk-import",
+		sourceManagerMode: panelView.mode === "source-manager",
+		isRightPanelFolded,
+		pinnedCreatureId,
+		isWideDesktop,
+		showCreature,
+		showBulkImport,
+		showSourceManager,
+		dismissPanel,
+		toggleFold,
+		togglePin,
+		unpin,
+	};
+}