Remove unit capture event messages

Drop the "Your {unit} was captured by {name}" and "Captured {unit} from
{name}" display messages on unit ownership change in UnitImpl. They fired
on every capture — dominated by warships taking trade ships — and were
too spammy to be useful, so players tuned them out.

Also clean up the now-unused pieces:
- Remove the UNIT_CAPTURED_BY_ENEMY message type, its category mapping,
  and its case in getMessageTypeClasses.
- Remove the orphaned unit_captured_by_enemy and captured_enemy_unit
  en.json keys.

CAPTURED_ENEMY_UNIT is kept — still used by the trade-ship gold message.

resources/lang/en.json

@@ -1135,8 +1135,6 @@
     "received_troops_from_player": "Received {troops} troops from {name}",
     "sent_gold_to_player": "Sent {gold} gold to {name}",
     "received_gold_from_player": "Received {gold} gold from {name}",
-    "unit_captured_by_enemy": "Your {unit} was captured by {name}",
-    "captured_enemy_unit": "Captured {unit} from {name}",
     "unit_destroyed": "Your {unit} was destroyed",
     "no_boats_available": "No boats available, max {max}"
   },

src/client/Utils.ts

@@ -516,7 +516,6 @@ export function getMessageTypeClasses(type: MessageType): string {
     case MessageType.ATTACK_FAILED:
     case MessageType.ALLIANCE_REJECTED:
     case MessageType.ALLIANCE_BROKEN:
-    case MessageType.UNIT_CAPTURED_BY_ENEMY:
     case MessageType.UNIT_DESTROYED:
     case MessageType.NUKE_DETONATED:
       return severityColors["fail"];

src/core/game/Game.ts

@@ -1063,7 +1063,6 @@ export enum MessageType {
   SAM_MISS,
   SAM_HIT,
   CAPTURED_ENEMY_UNIT,
-  UNIT_CAPTURED_BY_ENEMY,
   UNIT_DESTROYED,
   ALLIANCE_ACCEPTED,
   ALLIANCE_REJECTED,
@@ -1099,7 +1098,6 @@ export const MESSAGE_TYPE_CATEGORIES: Record<MessageType, MessageCategory> = {
   [MessageType.SAM_MISS]: MessageCategory.ATTACK,
   [MessageType.SAM_HIT]: MessageCategory.ATTACK,
   [MessageType.CAPTURED_ENEMY_UNIT]: MessageCategory.ATTACK,
-  [MessageType.UNIT_CAPTURED_BY_ENEMY]: MessageCategory.ATTACK,
   [MessageType.UNIT_DESTROYED]: MessageCategory.ATTACK,
   [MessageType.ALLIANCE_ACCEPTED]: MessageCategory.ALLIANCE,
   [MessageType.ALLIANCE_REJECTED]: MessageCategory.ALLIANCE,

src/core/game/UnitImpl.ts

@@ -213,22 +213,6 @@ export class UnitImpl implements Unit {
     this._owner = newOwner;
     this._owner._units.push(this);
     this.mg.addUpdate(this.toUpdate());
-    this.mg.displayMessage(
-      "events_display.unit_captured_by_enemy",
-      MessageType.UNIT_CAPTURED_BY_ENEMY,
-      this._lastOwner.id(),
-      undefined,
-      { unit: this.type(), name: newOwner.displayName() },
-      this.id(),
-    );
-    this.mg.displayMessage(
-      "events_display.captured_enemy_unit",
-      MessageType.CAPTURED_ENEMY_UNIT,
-      newOwner.id(),
-      undefined,
-      { unit: this.type(), name: this._lastOwner.displayName() },
-      this.id(),
-    );
   }
 
   modifyHealth(delta: number, attacker?: Player): void {