fix: preserve boss first-kill state across prestige

Fixes #39. Added bountyRunestonesClaimed?: boolean to the Boss type.
The first-kill bounty runestones are now only awarded once across all
prestige resets — the boss route checks the flag before awarding, sets
it on first defeat, and buildPostPrestigeState carries the flag forward
through fresh boss state on prestige. The boss panel badge no longer
shows for bosses whose bounty has already been claimed.

apps/api/test/routes/boss.spec.ts

@@ -305,4 +305,25 @@ describe("boss route", () => {
     const res = await challenge({ bossId: "test_boss" });
     expect(res.status).toBe(500);
   });
+
+  it("does not re-award bounty runestones when bountyRunestonesClaimed is true", async () => {
+    const state = makeState({
+      bosses: [makeBoss({
+        bountyRunestonesClaimed: true,
+        currentHp:               100,
+        damagePerSecond:         1,
+        maxHp:                   100,
+      })] as GameState["bosses"],
+      adventurers: [makeAdventurer()] as GameState["adventurers"],
+      prestige:    { count: 0, productionMultiplier: 1, purchasedUpgradeIds: [], runestones: 5 },
+      zones:       [],
+    });
+    vi.mocked(prisma.gameState.findUnique).mockResolvedValueOnce({ state } as never);
+    vi.mocked(prisma.gameState.update).mockResolvedValueOnce({} as never);
+    const res = await challenge({ bossId: "test_boss" });
+    expect(res.status).toBe(200);
+    const body = await res.json() as { won: boolean; rewards: { bountyRunestones: number } };
+    expect(body.won).toBe(true);
+    expect(body.rewards.bountyRunestones).toBe(0);
+  });
 });

apps/api/test/services/prestige.spec.ts

@@ -292,6 +292,33 @@ describe("buildPostPrestigeState", () => {
     expect(prestigeState.player.lifetimeBossesDefeated).toBe(1);
   });
 
+  it("preserves bountyRunestonesClaimed flag on bosses across prestige", () => {
+    const claimedBoss = {
+      bountyRunestones:        5,
+      bountyRunestonesClaimed: true,
+      crystalReward:           0,
+      currentHp:               0,
+      damagePerSecond:         10,
+      description:             "A boss",
+      equipmentRewards:        [] as string[],
+      essenceReward:           0,
+      goldReward:              100,
+      id:                      "troll_king",
+      maxHp:                   100,
+      name:                    "Troll King",
+      prestigeRequirement:     0,
+      status:                  "defeated" as const,
+      upgradeRewards:          [] as string[],
+      zoneId:                  "verdant_vale",
+    };
+    const state = makeMinimalState({ bosses: [ claimedBoss ] as GameState["bosses"] });
+    const { prestigeState } = buildPostPrestigeState(state, "Tester");
+    const matchingBoss = prestigeState.bosses.find((boss) => {
+      return boss.id === "troll_king";
+    });
+    expect(matchingBoss?.bountyRunestonesClaimed).toBe(true);
+  });
+
   it("accumulates completed quests into lifetime total", () => {
     const quest = {
       id:          "q_1",