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/creature-initiative-modifier.ts

@@ -0,0 +1,21 @@
+import {
+	type AnyCreature,
+	calculateInitiative,
+	calculatePf2eInitiative,
+} from "@initiative/domain";
+
+export function creatureInitiativeModifier(creature: AnyCreature): number {
+	if ("system" in creature && creature.system === "pf2e") {
+		return calculatePf2eInitiative(creature.perception).modifier;
+	}
+	const c = creature as {
+		abilities: { dex: number };
+		cr: string;
+		initiativeProficiency: number;
+	};
+	return calculateInitiative({
+		dexScore: c.abilities.dex,
+		cr: c.cr,
+		initiativeProficiency: c.initiativeProficiency,
+	}).modifier;
+}