Change quest reward from minerals to credits

- Replace the 250 mineral reward with a flat 200 credit payout
- Update the accompanying comment to reflect the new reward type and value

data/quests.json

@@ -131,8 +131,8 @@
         { "type": "trestleMet", "label": "Meet Trestle in the neighboring system" }
       ],
       "reward": {
-        "minerals": 250,
-        "_comment": "The completion reward — the ship's full hold (ship.stats.mineralStorage), claimed via the CLAIM REWARD action."
+        "credits": 200,
+        "_comment": "The completion reward — 200 Credits, claimed via the CLAIM REWARD action."
       }
     }
   ]