♻️ resource-based passability: FOREST/ROCK walkable without a resource (Issue #22)

Previously FOREST and ROCK tile types were always impassable, making 30 % of
forest floor and 50 % of rocky terrain permanently blocked even with no object
on them.

- Remove FOREST + ROCK from IMPASSABLE in types.ts
- Add RESOURCE_TERRAIN set (FOREST, ROCK) for tiles that need resource check
- WorldSystem: add resourceTiles Set<number> as O(1) spatial index
  - initResourceTiles() builds index from state on create()
  - addResourceTile() / removeResourceTile() keep it in sync at runtime
- isPassable() now: impassable tiles → false | RESOURCE_TERRAIN → check index | else → true
- GameScene: call addResourceTile() when SPAWN_RESOURCE fires (seedling matures)
- VillagerSystem: call removeResourceTile() after chop / mine completes

Side effect: trees fully enclosed by other trees are now reachable once an
adjacent tree is cleared; the hasAdjacentPassable() guard in pickJob still
correctly skips resources with zero passable neighbours.

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

src/systems/WorldSystem.ts

@@ -1,6 +1,6 @@
 import Phaser from 'phaser'
 import { TILE_SIZE, WORLD_TILES } from '../config'
-import { TileType, IMPASSABLE } from '../types'
+import { TileType, IMPASSABLE, RESOURCE_TERRAIN } from '../types'
 import { stateManager } from '../StateManager'
 
 const BIOME_COLORS: Record<number, string> = {
@@ -18,6 +18,12 @@ const BIOME_COLORS: Record<number, string> = {
 export class WorldSystem {
   private scene: Phaser.Scene
   private map!: Phaser.Tilemaps.Tilemap
+  /**
+   * Spatial index: tile keys (tileY * WORLD_TILES + tileX) for every tile
+   * that is currently occupied by a tree or rock resource.
+   * Used by isPassable() to decide if a FOREST or ROCK terrain tile is blocked.
+   */
+  private resourceTiles = new Set<number>()
   private tileset!: Phaser.Tilemaps.Tileset
   private bgImage!: Phaser.GameObjects.Image
   private builtLayer!: Phaser.Tilemaps.TilemapLayer
@@ -85,6 +91,8 @@ export class WorldSystem {
 
     // Camera bounds
     this.scene.cameras.main.setBounds(0, 0, WORLD_TILES * TILE_SIZE, WORLD_TILES * TILE_SIZE)
+
+    this.initResourceTiles()
   }
 
   /** Returns the built-tile tilemap layer (floor, wall, soil). */
@@ -111,6 +119,10 @@ export class WorldSystem {
 
   /**
    * Returns whether the tile at the given coordinates can be walked on.
+   * Water and wall tiles are always impassable.
+   * Forest and rock terrain tiles are only impassable when a resource
+   * (tree or rock) currently occupies them — empty forest floor and bare
+   * rocky ground are walkable.
    * Out-of-bounds tiles are treated as impassable.
    * @param tileX - Tile column
    * @param tileY - Tile row
@@ -119,7 +131,45 @@ export class WorldSystem {
     if (tileX < 0 || tileY < 0 || tileX >= WORLD_TILES || tileY >= WORLD_TILES) return false
     const state = stateManager.getState()
     const tile = state.world.tiles[tileY * WORLD_TILES + tileX]
-    return !IMPASSABLE.has(tile)
+    if (IMPASSABLE.has(tile)) return false
+    if (RESOURCE_TERRAIN.has(tile)) {
+      return !this.resourceTiles.has(tileY * WORLD_TILES + tileX)
+    }
+    return true
+  }
+
+  /**
+   * Builds the resource tile index from the current world state.
+   * Called once in create() so that isPassable() has an O(1) lookup.
+   */
+  private initResourceTiles(): void {
+    this.resourceTiles.clear()
+    const state = stateManager.getState()
+    for (const res of Object.values(state.world.resources)) {
+      this.resourceTiles.add(res.tileY * WORLD_TILES + res.tileX)
+    }
+  }
+
+  /**
+   * Registers a newly placed resource so isPassable() treats the tile as blocked.
+   * Call this whenever a resource is added at runtime (e.g. a seedling matures).
+   * @param tileX - Resource tile column
+   * @param tileY - Resource tile row
+   */
+  addResourceTile(tileX: number, tileY: number): void {
+    this.resourceTiles.add(tileY * WORLD_TILES + tileX)
+  }
+
+  /**
+   * Removes a resource from the tile index so isPassable() treats the tile as free.
+   * Call this when a resource is removed at runtime (e.g. after chopping/mining).
+   * Not strictly required when the tile type also changes (FOREST → DARK_GRASS),
+   * but keeps the index clean for correctness.
+   * @param tileX - Resource tile column
+   * @param tileY - Resource tile row
+   */
+  removeResourceTile(tileX: number, tileY: number): void {
+    this.resourceTiles.delete(tileY * WORLD_TILES + tileX)
   }
 
   /**