Add 2014 DMG encounter difficulty calculation

Support the 2014 DMG encounter difficulty as an alternative to the 5.5e
system behind the existing Rules Edition toggle. The 2014 system uses
Easy/Medium/Hard/Deadly thresholds, an encounter multiplier based on
monster count, and party size adjustment (×0.5–×5 range).

- Extract RulesEdition to its own domain module
- Refactor DifficultyTier to abstract numeric values (0–3)
- Restructure DifficultyResult with thresholds array
- Add 2014 XP thresholds table and encounter multiplier logic
- Wire edition from context into difficulty hooks
- Edition-aware labels in indicator and breakdown panel
- Show multiplier, adjusted XP, and party size note for 2014
- Rename settings label from "Conditions" to "Rules Edition"
- Update spec 008 with issue #23 requirements

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

apps/web/src/hooks/use-difficulty-breakdown.ts

@@ -1,6 +1,7 @@
 import type {
 	Combatant,
 	CreatureId,
+	DifficultyThreshold,
 	DifficultyTier,
 	PlayerCharacter,
 } from "@initiative/domain";
@@ -9,6 +10,7 @@ import { useMemo } from "react";
 import { useBestiaryContext } from "../contexts/bestiary-context.js";
 import { useEncounterContext } from "../contexts/encounter-context.js";
 import { usePlayerCharactersContext } from "../contexts/player-characters-context.js";
+import { useRulesEditionContext } from "../contexts/rules-edition-context.js";
 import { resolveSide } from "./use-difficulty.js";
 
 export interface BreakdownCombatant {
@@ -24,11 +26,10 @@ export interface BreakdownCombatant {
 interface DifficultyBreakdown {
 	readonly tier: DifficultyTier;
 	readonly totalMonsterXp: number;
-	readonly partyBudget: {
-		readonly low: number;
-		readonly moderate: number;
-		readonly high: number;
-	};
+	readonly thresholds: readonly DifficultyThreshold[];
+	readonly encounterMultiplier: number | undefined;
+	readonly adjustedXp: number | undefined;
+	readonly partySizeAdjusted: boolean | undefined;
 	readonly pcCount: number;
 	readonly partyCombatants: readonly BreakdownCombatant[];
 	readonly enemyCombatants: readonly BreakdownCombatant[];
@@ -38,6 +39,7 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 	const { encounter } = useEncounterContext();
 	const { characters } = usePlayerCharactersContext();
 	const { getCreature } = useBestiaryContext();
+	const { edition } = useRulesEditionContext();
 
 	return useMemo(() => {
 		const { partyCombatants, enemyCombatants, descriptors, pcCount } =
@@ -50,7 +52,7 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 
 		if (!hasPartyLevel || !hasCr) return null;
 
-		const result = calculateEncounterDifficulty(descriptors);
+		const result = calculateEncounterDifficulty(descriptors, edition);
 
 		return {
 			...result,
@@ -58,7 +60,7 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 			partyCombatants,
 			enemyCombatants,
 		};
-	}, [encounter.combatants, characters, getCreature]);
+	}, [encounter.combatants, characters, getCreature, edition]);
 }
 
 type CreatureInfo = {