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>

packages/application/src/roll-initiative-use-case.ts

@@ -1,8 +1,7 @@
 import {
+	type AnyCreature,
 	type CombatantId,
-	type Creature,
 	type CreatureId,
-	calculateInitiative,
 	type DomainError,
 	type DomainEvent,
 	isDomainError,
@@ -11,13 +10,14 @@ import {
 	selectRoll,
 	setInitiative,
 } from "@initiative/domain";
+import { creatureInitiativeModifier } from "./creature-initiative-modifier.js";
 import type { EncounterStore } from "./ports.js";
 
 export function rollInitiativeUseCase(
 	store: EncounterStore,
 	combatantId: CombatantId,
 	diceRolls: readonly [number, ...number[]],
-	getCreature: (id: CreatureId) => Creature | undefined,
+	getCreature: (id: CreatureId) => AnyCreature | undefined,
 	mode: RollMode = "normal",
 ): DomainEvent[] | DomainError {
 	const encounter = store.get();
@@ -48,11 +48,7 @@ export function rollInitiativeUseCase(
 		};
 	}
 
-	const { modifier } = calculateInitiative({
-		dexScore: creature.abilities.dex,
-		cr: creature.cr,
-		initiativeProficiency: creature.initiativeProficiency,
-	});
+	const modifier = creatureInitiativeModifier(creature);
 	const effectiveRoll =
 		mode === "normal"
 			? diceRolls[0]