✨ implement unified tile system (Issue #14)

- Tree seedlings: plant tree_seed on grass via farming tool; two-stage
  growth (sprout → sapling → young tree, ~1 min/stage); matures into
  a harvestable FOREST resource tile
- Tile recovery: Nisse chops start a 5-min DARK_GRASS→GRASS timer;
  terrain canvas updated live via WorldSystem.refreshTerrainTile()
- New TreeSeedlingSystem manages sprites, growth ticking, maturation
- BootScene generates seedling_0/1/2 textures procedurally
- FarmingSystem adds tree_seed to tool cycle (F key)
- Stockpile panel shows tree_seed (default: 5); panel height adjusted
- StateManager v5: treeSeedlings + tileRecovery in WorldState
- WorldSystem uses CanvasTexture for live single-pixel updates

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scenes/GameScene.ts

@@ -1,5 +1,6 @@
 import Phaser from 'phaser'
 import { AUTOSAVE_INTERVAL, TILE_SIZE } from '../config'
+import { TileType } from '../types'
 import type { BuildingType } from '../types'
 import { stateManager } from '../StateManager'
 import { LocalAdapter } from '../NetworkAdapter'
@@ -10,6 +11,7 @@ import { BuildingSystem } from '../systems/BuildingSystem'
 import { FarmingSystem } from '../systems/FarmingSystem'
 import { VillagerSystem } from '../systems/VillagerSystem'
 import { DebugSystem } from '../systems/DebugSystem'
+import { TreeSeedlingSystem } from '../systems/TreeSeedlingSystem'
 
 export class GameScene extends Phaser.Scene {
   private adapter!: LocalAdapter
@@ -20,6 +22,7 @@ export class GameScene extends Phaser.Scene {
   private farmingSystem!: FarmingSystem
   villagerSystem!: VillagerSystem
   debugSystem!: DebugSystem
+  private treeSeedlingSystem!: TreeSeedlingSystem
   private autosaveTimer = 0
   private menuOpen = false
 
@@ -37,9 +40,10 @@ export class GameScene extends Phaser.Scene {
     this.resourceSystem = new ResourceSystem(this, this.adapter)
     this.buildingSystem = new BuildingSystem(this, this.adapter)
     this.farmingSystem  = new FarmingSystem(this, this.adapter)
-    this.villagerSystem = new VillagerSystem(this, this.adapter, this.worldSystem)
+    this.villagerSystem      = new VillagerSystem(this, this.adapter, this.worldSystem)
     this.villagerSystem.init(this.resourceSystem, this.farmingSystem)
-    this.debugSystem    = new DebugSystem(this, this.villagerSystem, this.worldSystem)
+    this.treeSeedlingSystem  = new TreeSeedlingSystem(this, this.adapter, this.worldSystem)
+    this.debugSystem         = new DebugSystem(this, this.villagerSystem, this.worldSystem)
 
     this.worldSystem.create()
     this.renderPersistentObjects()
@@ -57,8 +61,12 @@ export class GameScene extends Phaser.Scene {
     }
 
     this.farmingSystem.create()
-    this.farmingSystem.onMessage    = (msg)         => this.events.emit('toast', msg)
-    this.farmingSystem.onToolChange = (tool, label) => this.events.emit('farmToolChanged', tool, label)
+    this.farmingSystem.onMessage     = (msg)         => this.events.emit('toast', msg)
+    this.farmingSystem.onToolChange  = (tool, label) => this.events.emit('farmToolChanged', tool, label)
+    this.farmingSystem.onPlantTreeSeed = (tileX, tileY, tile) =>
+      this.treeSeedlingSystem.plantSeedling(tileX, tileY, tile)
+
+    this.treeSeedlingSystem.create()
 
     this.villagerSystem.create()
     this.villagerSystem.onMessage    = (msg) => this.events.emit('toast', msg)
@@ -70,6 +78,8 @@ export class GameScene extends Phaser.Scene {
     this.adapter.onAction = (action) => {
       if (action.type === 'CHANGE_TILE') {
         this.worldSystem.setTile(action.tileX, action.tileY, action.tile)
+      } else if (action.type === 'SPAWN_RESOURCE') {
+        this.resourceSystem.spawnResourcePublic(action.resource)
       }
     }
 
@@ -102,9 +112,17 @@ export class GameScene extends Phaser.Scene {
 
     this.resourceSystem.update(delta)
     this.farmingSystem.update(delta)
+    this.treeSeedlingSystem.update(delta)
     this.villagerSystem.update(delta)
     this.debugSystem.update()
 
+    // Tick tile-recovery timers; refresh canvas for any tiles that reverted to GRASS
+    const recovered = stateManager.tickTileRecovery(delta)
+    for (const key of recovered) {
+      const [tx, ty] = key.split(',').map(Number)
+      this.worldSystem.refreshTerrainTile(tx, ty, TileType.GRASS)
+    }
+
     this.events.emit('cameraMoved', this.cameraSystem.getCenterTile())
     this.buildingSystem.update()
 
@@ -144,6 +162,7 @@ export class GameScene extends Phaser.Scene {
     this.resourceSystem.destroy()
     this.buildingSystem.destroy()
     this.farmingSystem.destroy()
+    this.treeSeedlingSystem.destroy()
     this.villagerSystem.destroy()
   }
 }