feat: implement bl space image (GET /api/v2/space/image)

[23prime]

Type

feat

Summary

Implement bl space image command to download the space icon image.

Changes

• Add GET /api/v2/space/image support in src/api/space.rs
• Add bl space image --output <path> subcommand in src/cmd/space/image.rs
• Add --output option (default: space_image.png or similar)
• Update docs: website/docs/commands.md, website/i18n/ja/...

Notes

Returns binary image data. Use --output to specify the save path.