chore(repo): 忽略本地导入与图标产物

[milome]

Summary

• stop versioning local design import artifacts under \src/imports/\
• stop versioning root icon exploration exports \icon-square.png\, \icon-transparent.png\, and \icon-zoom.png\
• add ignore rules so these local-only assets do not return to the index

Notes

• local files remain in the working tree; this PR only removes them from Git tracking
• no application runtime code changes are included in this PR