⚡ replace polling timers with sorted event queues + action log

Crops, tree seedlings, and tile recovery no longer iterate all entries
every frame. Each event stores an absolute gameTime timestamp (growsAt).
A sorted priority queue is drained each tick — only due items are touched.

WorldState now tracks gameTime (ms); stateManager.advanceTime(delta)
increments it each frame. Save version bumped 5→6 with migration.

Action log ring buffer (15 entries) added to LocalAdapter; shown in
the F3 debug panel under "Last Actions".

Closes #36
Closes #37

src/systems/TreeSeedlingSystem.ts

@@ -38,7 +38,8 @@ export class TreeSeedlingSystem {
    * @param delta - Frame delta in milliseconds
    */
   update(delta: number): void {
-    const advanced = stateManager.tickSeedlings(delta)
+    // Drain seedling growth queue (no delta — gameTime is advanced by GameScene)
+    const advanced = stateManager.tickSeedlings()
     for (const id of advanced) {
       const state = stateManager.getState()
       const seedling = state.world.treeSeedlings[id]
@@ -91,7 +92,7 @@ export class TreeSeedlingSystem {
     const seedling: TreeSeedlingState = {
       id, tileX, tileY,
       stage: 0,
-      stageTimerMs: TREE_SEEDLING_STAGE_MS,
+      growsAt: stateManager.getGameTime() + TREE_SEEDLING_STAGE_MS,
       underlyingTile,
     }