feat(03-02): add clearTiles method to GridManager

- Added clearTiles method that marks tiles as cleared
- Emits tile:cleared event for each cleared tile
- Calls deselectAll() after clearing tiles
- Enables CORE-05 (connected tiles disappear) and CORE-07 (cleared tiles become passable)

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

src/managers/GridManager.ts

@@ -109,6 +109,20 @@ export class GridManager {
     return this.tiles;
   }
 
+  /**
+   * Clear tiles (mark as cleared and emit events)
+   * @param tiles - Array of tiles to clear
+   */
+  clearTiles(tiles: Tile[]): void {
+    tiles.forEach(tile => {
+      tile.cleared = true;
+      this.events.emit('tile:cleared', { tile });
+    });
+
+    // Clear selection after clearing tiles
+    this.deselectAll();
+  }
+
   /**
    * Get the event emitter for external subscription
    */