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/__tests__/rehydrate-combatant.test.ts

@@ -35,7 +35,7 @@ describe("rehydrateCombatant", () => {
 			expect(result?.maxHp).toBe(7);
 			expect(result?.currentHp).toBe(5);
 			expect(result?.tempHp).toBe(3);
-			expect(result?.conditions).toEqual(["poisoned"]);
+			expect(result?.conditions).toEqual([{ id: "poisoned" }]);
 			expect(result?.isConcentrating).toBe(true);
 			expect(result?.creatureId).toBe("creature-goblin");
 			expect(result?.color).toBe("red");
@@ -165,7 +165,45 @@ describe("rehydrateCombatant", () => {
 				...minimalCombatant(),
 				conditions: ["poisoned", "fake", "blinded"],
 			});
-			expect(result?.conditions).toEqual(["poisoned", "blinded"]);
+			expect(result?.conditions).toEqual([
+				{ id: "poisoned" },
+				{ id: "blinded" },
+			]);
+		});
+
+		it("converts old bare string format to ConditionEntry", () => {
+			const result = rehydrateCombatant({
+				...minimalCombatant(),
+				conditions: ["blinded", "prone"],
+			});
+			expect(result?.conditions).toEqual([{ id: "blinded" }, { id: "prone" }]);
+		});
+
+		it("passes through new ConditionEntry format with values", () => {
+			const result = rehydrateCombatant({
+				...minimalCombatant(),
+				conditions: [{ id: "blinded" }, { id: "frightened", value: 2 }],
+			});
+			expect(result?.conditions).toEqual([
+				{ id: "blinded" },
+				{ id: "frightened", value: 2 },
+			]);
+		});
+
+		it("handles mixed old and new format entries", () => {
+			const result = rehydrateCombatant({
+				...minimalCombatant(),
+				conditions: ["blinded", { id: "prone" }],
+			});
+			expect(result?.conditions).toEqual([{ id: "blinded" }, { id: "prone" }]);
+		});
+
+		it("drops ConditionEntry with invalid value", () => {
+			const result = rehydrateCombatant({
+				...minimalCombatant(),
+				conditions: [{ id: "blinded", value: -1 }],
+			});
+			expect(result?.conditions).toEqual([{ id: "blinded" }]);
 		});
 
 		it("drops invalid color — keeps combatant", () => {