fix: prevent duplicate prestige bot announcements on concurrent requests

Adds an optimistic lock on the prestige route so that a second concurrent
request for the same state is rejected with 409 rather than firing the
Discord announcement twice. Also adds missing branch-coverage tests for
debug.ts to satisfy the 100% threshold.

Closes #162

apps/api/src/routes/prestige.ts

@@ -102,12 +102,23 @@ prestigeRouter.post("/", async(context) => {
     }).length;
 
     const now = Date.now();
-    await prisma.gameState.update({
+    const { updatedAt } = record;
+
+    /*
+     * Use the record's current updatedAt as an optimistic lock — if another
+     * concurrent prestige request already committed, this update will match
+     * 0 rows and we can safely reject the duplicate without a double webhook.
+     */
+    const updateResult = await prisma.gameState.updateMany({
       /* eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- Prisma requires object */
       data:  { state: finalState as object, updatedAt: now },
-      where: { discordId },
+      where: { discordId, updatedAt },
     });
 
+    if (updateResult.count === 0) {
+      return context.json({ error: "Prestige already in progress" }, 409);
+    }
+
     await prisma.player.update({
       data: {
         characterName: state.player.characterName,