Add advantage/disadvantage rolling for initiative

Right-click or long-press the d20 button (per-combatant or Roll All)
to open a context menu with Advantage and Disadvantage options.
Normal left-click behavior is unchanged.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/application/src/__tests__/roll-all-initiative-use-case.test.ts

@@ -161,6 +161,48 @@ describe("rollAllInitiativeUseCase", () => {
 		expect(store.saved).toBeNull();
 	});
 
+	it("uses higher roll with advantage", () => {
+		const enc = encounterWithCombatants([
+			{ name: "A", creatureId: "creature-a" },
+		]);
+		const store = stubEncounterStore(enc);
+		const creature = makeCreature("creature-a");
+
+		// Alternating rolls: 5, 15 → advantage picks 15
+		// Dex 14 → modifier +2, so 15 + 2 = 17
+		let call = 0;
+		const result = rollAllInitiativeUseCase(
+			store,
+			() => (++call % 2 === 1 ? 5 : 15),
+			(id) => (id === CREATURE_A ? creature : undefined),
+			"advantage",
+		);
+
+		expectSuccess(result);
+		expect(requireSaved(store.saved).combatants[0].initiative).toBe(17);
+	});
+
+	it("uses lower roll with disadvantage", () => {
+		const enc = encounterWithCombatants([
+			{ name: "A", creatureId: "creature-a" },
+		]);
+		const store = stubEncounterStore(enc);
+		const creature = makeCreature("creature-a");
+
+		// Alternating rolls: 15, 5 → disadvantage picks 5
+		// Dex 14 → modifier +2, so 5 + 2 = 7
+		let call = 0;
+		const result = rollAllInitiativeUseCase(
+			store,
+			() => (++call % 2 === 1 ? 15 : 5),
+			(id) => (id === CREATURE_A ? creature : undefined),
+			"disadvantage",
+		);
+
+		expectSuccess(result);
+		expect(requireSaved(store.saved).combatants[0].initiative).toBe(7);
+	});
+
 	it("saves encounter once at the end", () => {
 		const enc = encounterWithCombatants([
 			{ name: "A", creatureId: "creature-a" },