fix: preserve all-time stats, achievements, and boss first-kill across prestige (#47)

Resolves #37, resolves #38, and resolves #39 — three related bugs where prestige incorrectly reset data that should survive all prestige resets.

## Changes

### fix: preserve lifetime player stats across prestige (#37)
After prestige, `GameState.player.lifetime*` fields were stale — they reflected values from *before* the current run. The Prisma Player record was incremented correctly, but the GameState JSON saved to the DB had old values, so the UI showed wrong all-time totals on reload.

`buildPostPrestigeState` now computes the run-stat contributions (bosses defeated, quests completed, adventurers recruited, achievements unlocked, gold earned, clicks) and folds them into the fresh player object before writing the prestige state.

### fix: preserve achievements across prestige (#38)
`buildPostPrestigeState` was reconstructing achievements from `defaultAchievements` (via `initialGameState`), resetting all unlocked achievements on every prestige. Achievements are now carried forward from `currentState.achievements` instead.

### fix: preserve boss first-kill state across prestige (#39)
Added `bountyRunestonesClaimed?: boolean` to the `Boss` type. The boss challenge route now:
- Only awards the first-kill bounty runestones if `bountyRunestonesClaimed !== true`
- Sets `bountyRunestonesClaimed = true` on first defeat

`buildPostPrestigeState` maps the fresh boss list and carries the `bountyRunestonesClaimed` flag forward from the current state, so the bounty is never re-awarded in subsequent prestige runs. The boss panel badge is also hidden for bosses whose bounty is already claimed.

## Test Coverage
All three fixes include new tests covering the new behaviours. API coverage remains at 100%.

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #47
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/api/src/services/prestige.ts

@@ -205,10 +205,69 @@ const buildPostPrestigeState = (
   };
 
   const freshState = initialGameState(currentState.player, characterName);
+
+  /*
+   * Preserve first-kill (bounty claimed) status across the prestige reset so
+   * the one-time bounty is never re-awarded in subsequent runs.
+   */
+  const bossesWithBountyClaimed = freshState.bosses.map((freshBoss) => {
+    const currentBoss = currentState.bosses.find((candidate) => {
+      return candidate.id === freshBoss.id;
+    });
+    if (currentBoss?.bountyRunestonesClaimed === true) {
+      return { ...freshBoss, bountyRunestonesClaimed: true };
+    }
+    return freshBoss;
+  });
+
+  // Compute current-run contributions to accumulate into lifetime totals
+  const runBossesDefeated = currentState.bosses.filter((boss) => {
+    return boss.status === "defeated";
+  }).length;
+  const runQuestsCompleted = currentState.quests.filter((quest) => {
+    return quest.status === "completed";
+  }).length;
+  let runAdventurersRecruited = 0;
+  for (const adventurer of currentState.adventurers) {
+    runAdventurersRecruited = runAdventurersRecruited + adventurer.count;
+  }
+  const runAchievementsUnlocked = currentState.achievements.filter(
+    (achievement) => {
+      return achievement.unlockedAt !== null;
+    },
+  ).length;
+
   const prestigeState: GameState = {
     ...freshState,
-    lastTickAt: Date.now(),
-    prestige:   prestigeData,
+    // Achievements are permanent — earned achievements survive all prestiges
+    achievements: currentState.achievements,
+    // Boss statuses reset for gameplay, but first-kill claimed flag is preserved
+    bosses:       bossesWithBountyClaimed,
+    lastTickAt:   Date.now(),
+
+    /*
+     * Fold current-run totals into lifetime stats so the GameState reflects
+     * the true all-time values immediately after prestige.
+     */
+    player: {
+      ...freshState.player,
+      lifetimeAchievementsUnlocked:
+        freshState.player.lifetimeAchievementsUnlocked
+        + runAchievementsUnlocked,
+      lifetimeAdventurersRecruited:
+        freshState.player.lifetimeAdventurersRecruited
+        + runAdventurersRecruited,
+      lifetimeBossesDefeated:
+        freshState.player.lifetimeBossesDefeated + runBossesDefeated,
+      lifetimeClicks:
+        freshState.player.lifetimeClicks + currentState.player.totalClicks,
+      lifetimeGoldEarned:
+        freshState.player.lifetimeGoldEarned
+        + currentState.player.totalGoldEarned,
+      lifetimeQuestsCompleted:
+        freshState.player.lifetimeQuestsCompleted + runQuestsCompleted,
+    },
+    prestige: prestigeData,
     // Codex lore persists across prestiges — players keep their discovered entries
     ...currentState.codex === undefined
       ? {}