feat(init): 支持补齐内置模板空目录

新增 init 子命令，根据项目中的 world_*_packs.json 解析实际包目录并创建标准空目录。

改用 .empty-dirs 维护内置模板空目录清单，删除会污染用户项目和网易 Bedrock 加载流程的 .gitkeep 占位文件。

examples/default/.empty-dirs

@@ -0,0 +1,37 @@
+behavior_pack/BoxData
+behavior_pack/entities
+behavior_pack/items
+behavior_pack/loot_tables
+behavior_pack/netease_feature_rules
+behavior_pack/netease_features
+behavior_pack/netease_items_beh
+behavior_pack/Parts
+behavior_pack/Presets
+behavior_pack/recipes
+behavior_pack/spawn_rules
+behavior_pack/structures
+behavior_pack/trading
+behavior_pack/Galaxy/Macro
+behavior_pack/Galaxy/Template
+behavior_pack/storyline/level
+resource_pack/animation_controllers
+resource_pack/animations
+resource_pack/attachables
+resource_pack/effects
+resource_pack/entity
+resource_pack/font
+resource_pack/materials
+resource_pack/models/animation
+resource_pack/models/editor_materials
+resource_pack/models/effect
+resource_pack/models/geometry
+resource_pack/models/mesh
+resource_pack/models/netease_block
+resource_pack/render_controllers
+resource_pack/shaders/glsl
+resource_pack/sounds
+resource_pack/textures/entity
+resource_pack/textures/models
+resource_pack/textures/particle
+resource_pack/textures/ui
+resource_pack/ui