Gate random encounters on the 'Special Delivery' quest claim

- Add `_encountersLockedByQuest()` to GameScene: while the delivery
  chain is live (not yet completed AND claimed), keep the encounter
  director from rolling. Quests disabled = gate off too.
- AND the new scene-side hold into `encounters.update`'s `allowed` so
  the pure clock stays untouched; document the contract in Encounters.js.
- Ship new transport sprite assets (ships-transport.png/.psd).

js/combat/Encounters.js

@@ -8,8 +8,12 @@
  *
  *   WHEN — while the system allows encounters (NEUTRAL — faction null —,
  *     not home, no wave run in flight, the player upright; the scene
- *     passes `ctx.allowed`, `encounterAllowed` is the pure gate), a
- *     ROLL lands on the interval schedule (data/combat.json →
+ *     passes `ctx.allowed`, `encounterAllowed` is the pure gate) AND the
+ *     scene's own quest hold stands off — GameScene ANDs in
+ *     `_encountersLockedByQuest`, the 'Special Delivery' gate: the rolls
+ *     stay off until that quest is completed and claimed (a scene-side
+ *     state, so it never crosses this module's pure contract). A roll then
+ *     lands on the interval schedule (data/combat.json →
  *     encounters.rollIntervalMin..rollIntervalMax, seconds); each roll
  *     fires at chanceMin..chanceMax probability. ONE AT A TIME: the
  *     schedule holds while an encounter is engaged.

js/scenes/GameScene.js

@@ -2621,7 +2621,8 @@ export class GameScene extends Phaser.Scene {
         // returns the composition to spawn — off-screen, streamed in by
         // their own AI (the clock is pure; the scene stays the spawner).
         const comp = this.encounters.update(_time, {
-          allowed: encounterAllowed({
+          allowed:
+            encounterAllowed({
             ship: this.ship,
             isHomeSystem: this.isHomeSystem,
             faction: this.systemRecord ? this.systemRecord.faction : null,
@@ -2630,7 +2631,7 @@ export class GameScene extends Phaser.Scene {
               this.combat.waveRun.state !== 'done' &&
               this.combat.waveRun.state !== 'cancelled',
             playerDown: this.combat.playerDown,
-          }),
+          }) && !this._encountersLockedByQuest(), // the 'Special Delivery' hold
           live: this.combat.active,
           xpLevel: this.combat.xp.level,
         });
@@ -3754,6 +3755,22 @@ export class GameScene extends Phaser.Scene {
     return cap !== '' && cap === name;
   }
 
+  /**
+   * The random-encounter hold (the 'Special Delivery' gate): the run's
+   * first flights into neutral space stay calm while the delivery chain
+   * is live — the director rolls (EncounterDirector, the pure clock)
+   * only once 'Special Delivery' is COMPLETED AND CLAIMED (the same
+   * witness the run's chain uses — QuestState.isClaimed; the claim is
+   * the scene's own, paid out only on a fully satisfied quest). Quests
+   * off (the config kill-switch, data/game.json) = the gate is off too:
+   * with no quest there is nothing to wait on.
+   * @returns {boolean} true while random encounters stay locked
+   */
+  _encountersLockedByQuest() {
+    if (config.get('quests.enabled', true) === false) return false;
+    return this.questState?.isClaimed?.('special_delivery') !== true;
+  }
+
   /**
    * LAND (commsAction) — the surface sequence: SurfaceScene starts ON
    * TOP of this scene, handed the world's planets.png sheet frame so it