Add Pathfinder 2e game system mode

Implements PF2e as an alternative game system alongside D&D 5e/5.5e.
Settings modal "Game System" selector switches conditions, bestiary,
stat block layout, and initiative calculation between systems.

- Valued conditions with increment/decrement UX (Clumsy 2, Frightened 3)
- 2,502 PF2e creatures from bundled search index (77 sources)
- PF2e stat block: level, traits, Perception, Fort/Ref/Will, ability mods
- Perception-based initiative rolling
- System-scoped source cache (D&D and PF2e sources don't collide)
- Backwards-compatible condition rehydration (ConditionId[] → ConditionEntry[])
- Difficulty indicator hidden in PF2e mode (excluded from MVP)

Closes dostulata/initiative#19

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

apps/web/src/components/difficulty-breakdown-panel.tsx

@@ -11,9 +11,8 @@ import {
 import { CrPicker } from "./cr-picker.js";
 import { Button } from "./ui/button.js";
 
-const TIER_LABEL_MAP: Record<
-	RulesEdition,
-	Record<DifficultyTier, { label: string; color: string }>
+const TIER_LABEL_MAP: Partial<
+	Record<RulesEdition, Record<DifficultyTier, { label: string; color: string }>>
 > = {
 	"5.5e": {
 		0: { label: "Trivial", color: "text-muted-foreground" },
@@ -117,7 +116,9 @@ export function DifficultyBreakdownPanel({ onClose }: { onClose: () => void }) {
 	const breakdown = useDifficultyBreakdown();
 	if (!breakdown) return null;
 
-	const tierConfig = TIER_LABEL_MAP[edition][breakdown.tier];
+	const tierLabels = TIER_LABEL_MAP[edition];
+	if (!tierLabels) return null;
+	const tierConfig = tierLabels[breakdown.tier];
 
 	const handleToggle = (entry: BreakdownCombatant) => {
 		const newSide = entry.side === "party" ? "enemy" : "party";