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/domain/src/initiative.ts

@@ -20,6 +20,14 @@ export function calculateInitiative(creature: {
 	return { modifier, passive: 10 + modifier };
 }
 
+/**
+ * Returns the PF2e initiative result directly from the Perception modifier.
+ * No proficiency bonus calculation — PF2e uses Perception as-is.
+ */
+export function calculatePf2eInitiative(perception: number): InitiativeResult {
+	return { modifier: perception, passive: perception };
+}
+
 /**
  * Formats an initiative modifier with explicit sign.
  * Uses U+2212 (−) for negative values.