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/hooks/use-difficulty-breakdown.ts

@@ -64,7 +64,7 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 }
 
 type CreatureInfo = {
-	cr: string;
+	cr?: string;
 	source: string;
 	sourceDisplayName: string;
 };
@@ -87,10 +87,11 @@ function buildBreakdownEntry(
 		};
 	}
 	if (creature) {
+		const cr = creature.cr ?? null;
 		return {
 			combatant: c,
-			cr: creature.cr,
-			xp: crToXp(creature.cr),
+			cr,
+			xp: cr ? crToXp(cr) : null,
 			source: creature.sourceDisplayName ?? creature.source,
 			editable: false,
 			side,
@@ -132,7 +133,7 @@ function resolveCr(
 	getCreature: (id: CreatureId) => CreatureInfo | undefined,
 ): { cr: string | null; creature: CreatureInfo | undefined } {
 	const creature = c.creatureId ? getCreature(c.creatureId) : undefined;
-	const cr = creature ? creature.cr : (c.cr ?? null);
+	const cr = creature?.cr ?? c.cr ?? null;
 	return { cr, creature };
 }