✨ add demolish mode for buildings (Issue #50)

- New 💥 Demolish button in the action bar
- Red ghost highlights building footprint on hover
- Refund: 100% within 3 min, decays linearly to 0%
- Mine teardown unblocks passability tiles and removes status label
- Nisse inside demolished mine are rescued and reset to idle
- Floor/wall/chest tiles restored to GRASS on demolish
- Build error now shows missing resources instead of generic message
- BuildingState gains builtAt field; old saves default to 0 (no refund)

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

src/systems/VillagerSystem.ts

@@ -767,6 +767,33 @@ export class VillagerSystem {
    * Destroys all Nisse sprites and clears the runtime map.
    * Should be called when the scene shuts down.
    */
+  /**
+   * Rescues all Nisse that were working inside a demolished building.
+   * Makes hidden sprites visible again, clears their jobs, and resets AI to idle.
+   * Also releases any mine-capacity claims for that building.
+   * @param buildingId - ID of the building that was demolished
+   */
+  rescueNisseFromBuilding(buildingId: string): void {
+    this.mineClaimsMap.delete(buildingId)
+    const state = stateManager.getState()
+    for (const v of Object.values(state.world.villagers)) {
+      if (v.job?.targetId !== buildingId) continue
+      const rt = this.runtime.get(v.id)
+      if (!rt) continue
+      // Make sprite visible in case the Nisse was hidden inside the mine
+      rt.sprite.setVisible(true)
+      rt.nameLabel.setVisible(true)
+      rt.energyBar.setVisible(true)
+      rt.jobIcon.setVisible(true)
+      rt.workTimer = 0
+      rt.idleScanTimer = 0
+      this.claimed.delete(buildingId)
+      this.adapter.send({ type: 'VILLAGER_SET_JOB', villagerId: v.id, job: null })
+      this.adapter.send({ type: 'VILLAGER_SET_AI', villagerId: v.id, aiState: 'idle' })
+      this.addLog(v.id, '! Building demolished — resuming')
+    }
+  }
+
   /**
    * Destroys all Nisse sprites and clears the runtime map.
    * Should be called when the scene shuts down.