feat: resource collection with E-key interaction (Phase 4.3)

Mineral veins yield metals (Fe, Cu, Zn, Au, Sn), geysers yield S/H.
Resources spawn as ECS entities with gold/orange dot sprites on tiles.
E-key collects nearest resource in range into inventory. Resources
deplete after collection. Visual feedback text. 12 new tests (174 total).

Co-authored-by: Cursor <cursoragent@cursor.com>

src/world/resources.ts

@@ -0,0 +1,106 @@
+/**
+ * Resource Spawner — creates ECS entities for harvestable world objects
+ *
+ * Scans the generated tile grid for mineral veins and geysers,
+ * creates an entity at each with a randomly assigned element.
+ */
+
+import { addEntity, addComponent } from 'bitecs';
+import type { World } from '../ecs/world';
+import { Position, Resource, SpriteRef } from '../ecs/components';
+import type { TileGrid, BiomeData } from './types';
+import {
+  pickResourceElement,
+  MINERAL_ELEMENTS,
+  GEYSER_ELEMENTS,
+  type ResourceInfo,
+} from '../player/interaction';
+
+/** Resource spawn configuration per tile type */
+interface ResourceTileConfig {
+  tileId: number;
+  elements: readonly string[];
+  minQuantity: number;
+  maxQuantity: number;
+  interactRange: number;
+  spriteColor: number;
+  spriteRadius: number;
+}
+
+/**
+ * Spawn resource entities for all resource tiles in the grid.
+ * @returns Map of entity ID → ResourceInfo for string data
+ */
+export function spawnResources(
+  world: World,
+  grid: TileGrid,
+  biome: BiomeData,
+  seed: number,
+): Map<number, ResourceInfo> {
+  const resourceData = new Map<number, ResourceInfo>();
+
+  // Find tile IDs for resource types
+  const mineralTile = biome.tiles.find(t => t.name === 'mineral-vein');
+  const geyserTile = biome.tiles.find(t => t.name === 'geyser');
+
+  const configs: ResourceTileConfig[] = [];
+
+  if (mineralTile) {
+    configs.push({
+      tileId: mineralTile.id,
+      elements: MINERAL_ELEMENTS,
+      minQuantity: 3,
+      maxQuantity: 5,
+      interactRange: 40,
+      spriteColor: 0xffd700, // gold
+      spriteRadius: 4,
+    });
+  }
+
+  if (geyserTile) {
+    configs.push({
+      tileId: geyserTile.id,
+      elements: GEYSER_ELEMENTS,
+      minQuantity: 2,
+      maxQuantity: 4,
+      interactRange: 48,
+      spriteColor: 0xff6600, // orange
+      spriteRadius: 5,
+    });
+  }
+
+  const tileSize = biome.tileSize;
+
+  for (let y = 0; y < grid.length; y++) {
+    for (let x = 0; x < grid[y].length; x++) {
+      const tileId = grid[y][x];
+      const config = configs.find(c => c.tileId === tileId);
+      if (!config) continue;
+
+      // Pick element deterministically
+      const itemId = pickResourceElement(x, y, seed, config.elements);
+
+      // Quantity from deterministic hash
+      const qHash = ((x * 48611) ^ (y * 29423) ^ (seed * 61379)) >>> 0;
+      const range = config.maxQuantity - config.minQuantity + 1;
+      const quantity = config.minQuantity + (qHash % range);
+
+      // Create entity at tile center
+      const eid = addEntity(world);
+      addComponent(world, eid, Position);
+      addComponent(world, eid, Resource);
+      addComponent(world, eid, SpriteRef);
+
+      Position.x[eid] = x * tileSize + tileSize / 2;
+      Position.y[eid] = y * tileSize + tileSize / 2;
+      Resource.quantity[eid] = quantity;
+      Resource.interactRange[eid] = config.interactRange;
+      SpriteRef.color[eid] = config.spriteColor;
+      SpriteRef.radius[eid] = config.spriteRadius;
+
+      resourceData.set(eid, { itemId, tileX: x, tileY: y });
+    }
+  }
+
+  return resourceData;
+}