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/__tests__/use-rules-edition.test.ts

@@ -1,9 +1,10 @@
 // @vitest-environment jsdom
 import { act, renderHook } from "@testing-library/react";
-import { afterEach, describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { useRulesEdition } from "../use-rules-edition.js";
 
-const STORAGE_KEY = "initiative:rules-edition";
+const STORAGE_KEY = "initiative:game-system";
+const OLD_STORAGE_KEY = "initiative:rules-edition";
 
 describe("useRulesEdition", () => {
 	afterEach(() => {
@@ -11,6 +12,7 @@ describe("useRulesEdition", () => {
 		const { result } = renderHook(() => useRulesEdition());
 		act(() => result.current.setEdition("5.5e"));
 		localStorage.removeItem(STORAGE_KEY);
+		localStorage.removeItem(OLD_STORAGE_KEY);
 	});
 
 	it("defaults to 5.5e", () => {
@@ -42,4 +44,31 @@ describe("useRulesEdition", () => {
 
 		expect(r2.current.edition).toBe("5e");
 	});
+
+	it("accepts pf2e as a valid game system", () => {
+		const { result } = renderHook(() => useRulesEdition());
+
+		act(() => result.current.setEdition("pf2e"));
+
+		expect(result.current.edition).toBe("pf2e");
+		expect(localStorage.getItem(STORAGE_KEY)).toBe("pf2e");
+	});
+
+	it("migrates from old storage key on fresh module load", async () => {
+		// Set up old key before re-importing the module
+		localStorage.setItem(OLD_STORAGE_KEY, "5e");
+		localStorage.removeItem(STORAGE_KEY);
+
+		// Force a fresh module so loadEdition() re-runs at init time
+		vi.resetModules();
+		const { useRulesEdition: freshHook } = await import(
+			"../use-rules-edition.js"
+		);
+
+		const { result } = renderHook(() => freshHook());
+
+		expect(result.current.edition).toBe("5e");
+		expect(localStorage.getItem(STORAGE_KEY)).toBe("5e");
+		expect(localStorage.getItem(OLD_STORAGE_KEY)).toBeNull();
+	});
 });