Add PF2e encounter difficulty calculation with 5-tier budget system

Implements PF2e encounter difficulty alongside the existing D&D system.
PF2e uses creature level vs party level to derive XP, compares against
5-tier budgets (Trivial/Low/Moderate/Severe/Extreme), and adjusts
thresholds for party size. The indicator shows 4 bars in PF2e mode.

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

apps/web/src/hooks/__tests__/use-difficulty.test.tsx

@@ -1,5 +1,9 @@
 // @vitest-environment jsdom
-import type { Creature, CreatureId, PlayerCharacter } from "@initiative/domain";
+import type {
+	AnyCreature,
+	CreatureId,
+	PlayerCharacter,
+} from "@initiative/domain";
 import { combatantId, creatureId, playerCharacterId } from "@initiative/domain";
 import { renderHook, waitFor } from "@testing-library/react";
 import type { ReactNode } from "react";
@@ -9,6 +13,7 @@ import {
 	buildCombatant,
 	buildCreature,
 	buildEncounter,
+	buildPf2eCreature,
 } from "../../__tests__/factories/index.js";
 import { AllProviders } from "../../__tests__/test-providers.js";
 import { useDifficulty } from "../use-difficulty.js";
@@ -43,7 +48,7 @@ const goblinCreature = buildCreature({
 function makeWrapper(options: {
 	encounter: ReturnType<typeof buildEncounter>;
 	playerCharacters?: PlayerCharacter[];
-	creatures?: Map<CreatureId, Creature>;
+	creatures?: Map<CreatureId, AnyCreature>;
 }) {
 	const adapters = createTestAdapters({
 		encounter: options.encounter,
@@ -424,4 +429,134 @@ describe("useDifficulty", () => {
 			expect(result.current?.totalMonsterXp).toBe(0);
 		});
 	});
+
+	describe("PF2e edition", () => {
+		const pf2eCreature = buildPf2eCreature({
+			id: creatureId("pf2e:orc-warrior"),
+			name: "Orc Warrior",
+			level: 5,
+		});
+
+		function makePf2eWrapper(options: {
+			encounter: ReturnType<typeof buildEncounter>;
+			playerCharacters?: PlayerCharacter[];
+			creatures?: Map<CreatureId, AnyCreature>;
+		}) {
+			const adapters = createTestAdapters({
+				encounter: options.encounter,
+				playerCharacters: options.playerCharacters ?? [],
+				creatures: options.creatures,
+			});
+			return ({ children }: { children: ReactNode }) => (
+				<AllProviders adapters={adapters}>{children}</AllProviders>
+			);
+		}
+
+		it("returns result for PF2e with leveled PCs and PF2e creatures", async () => {
+			const wrapper = makePf2eWrapper({
+				encounter: buildEncounter({
+					combatants: [
+						buildCombatant({
+							id: combatantId("c1"),
+							name: "Hero",
+							playerCharacterId: pcId1,
+						}),
+						buildCombatant({
+							id: combatantId("c2"),
+							name: "Orc Warrior",
+							creatureId: pf2eCreature.id,
+						}),
+					],
+				}),
+				playerCharacters: [
+					{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+				],
+				creatures: new Map([[pf2eCreature.id, pf2eCreature]]),
+			});
+
+			const { result: editionResult } = renderHook(() => useRulesEdition(), {
+				wrapper,
+			});
+			editionResult.current.setEdition("pf2e");
+
+			try {
+				const { result } = renderHook(() => useDifficulty(), { wrapper });
+
+				await waitFor(() => {
+					expect(result.current).not.toBeNull();
+					// Creature level 5, party level 5 → diff 0 → 40 XP
+					expect(result.current?.totalMonsterXp).toBe(40);
+					expect(result.current?.partyLevel).toBe(5);
+				});
+			} finally {
+				editionResult.current.setEdition("5.5e");
+			}
+		});
+
+		it("returns null for PF2e when no PF2e creatures with level", () => {
+			const wrapper = makePf2eWrapper({
+				encounter: buildEncounter({
+					combatants: [
+						buildCombatant({
+							id: combatantId("c1"),
+							name: "Hero",
+							playerCharacterId: pcId1,
+						}),
+						buildCombatant({
+							id: combatantId("c2"),
+							name: "Custom Monster",
+						}),
+					],
+				}),
+				playerCharacters: [
+					{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+				],
+			});
+
+			const { result: editionResult } = renderHook(() => useRulesEdition(), {
+				wrapper,
+			});
+			editionResult.current.setEdition("pf2e");
+
+			try {
+				const { result } = renderHook(() => useDifficulty(), { wrapper });
+				expect(result.current).toBeNull();
+			} finally {
+				editionResult.current.setEdition("5.5e");
+			}
+		});
+
+		it("returns null for PF2e when no PCs with level", () => {
+			const wrapper = makePf2eWrapper({
+				encounter: buildEncounter({
+					combatants: [
+						buildCombatant({
+							id: combatantId("c1"),
+							name: "Hero",
+							playerCharacterId: pcId1,
+						}),
+						buildCombatant({
+							id: combatantId("c2"),
+							name: "Orc Warrior",
+							creatureId: pf2eCreature.id,
+						}),
+					],
+				}),
+				playerCharacters: [{ id: pcId1, name: "Hero", ac: 15, maxHp: 30 }],
+				creatures: new Map([[pf2eCreature.id, pf2eCreature]]),
+			});
+
+			const { result: editionResult } = renderHook(() => useRulesEdition(), {
+				wrapper,
+			});
+			editionResult.current.setEdition("pf2e");
+
+			try {
+				const { result } = renderHook(() => useDifficulty(), { wrapper });
+				expect(result.current).toBeNull();
+			} finally {
+				editionResult.current.setEdition("5.5e");
+			}
+		});
+	});
 });