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/components/difficulty-indicator.tsx

@@ -1,27 +1,44 @@
 import type { DifficultyResult, DifficultyTier } from "@initiative/domain";
 import { cn } from "../lib/utils.js";
 
-const TIER_CONFIG: Record<
+export const TIER_LABELS_5_5E: Record<DifficultyTier, string> = {
+	0: "Trivial",
+	1: "Low",
+	2: "Moderate",
+	3: "High",
+};
+
+export const TIER_LABELS_2014: Record<DifficultyTier, string> = {
+	0: "Easy",
+	1: "Medium",
+	2: "Hard",
+	3: "Deadly",
+};
+
+const TIER_COLORS: Record<
 	DifficultyTier,
-	{ filledBars: number; color: string; label: string }
+	{ filledBars: number; color: string }
 > = {
-	trivial: { filledBars: 0, color: "", label: "Trivial" },
-	low: { filledBars: 1, color: "bg-green-500", label: "Low" },
-	moderate: { filledBars: 2, color: "bg-yellow-500", label: "Moderate" },
-	high: { filledBars: 3, color: "bg-red-500", label: "High" },
+	0: { filledBars: 0, color: "" },
+	1: { filledBars: 1, color: "bg-green-500" },
+	2: { filledBars: 2, color: "bg-yellow-500" },
+	3: { filledBars: 3, color: "bg-red-500" },
 };
 
 const BAR_HEIGHTS = ["h-2", "h-3", "h-4"] as const;
 
 export function DifficultyIndicator({
 	result,
+	labels,
 	onClick,
 }: {
 	result: DifficultyResult;
+	labels: Record<DifficultyTier, string>;
 	onClick?: () => void;
 }) {
-	const config = TIER_CONFIG[result.tier];
-	const tooltip = `${config.label} encounter difficulty`;
+	const config = TIER_COLORS[result.tier];
+	const label = labels[result.tier];
+	const tooltip = `${label} encounter difficulty`;
 
 	const Element = onClick ? "button" : "div";