chore(editor): update loading css vars (#12557)

Related to: [BS-3559](https://linear.app/affine-design/issue/BS-3559/ui-%E5%9B%BE%E7%89%87-loading-%E5%8F%98%E9%87%8F%E6%9B%B4%E6%96%B0)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Style**
  - Improved the appearance of image loading indicators by updating background and ring colors for a more consistent visual experience.

- **New Features**
  - Added customization options for the loading icon's ring color.

- **Chores**
  - Updated the "@toeverything/theme" dependency to version ^1.1.15 across multiple packages for improved consistency and compatibility.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/shared/package.json

@@ -18,7 +18,7 @@
     "@floating-ui/dom": "^1.6.13",
     "@lit/context": "^1.1.2",
     "@preact/signals-core": "^1.8.0",
-    "@toeverything/theme": "^1.1.14",
+    "@toeverything/theme": "^1.1.15",
     "@types/bytes": "^3.1.5",
     "@types/hast": "^3.0.4",
     "@types/lodash-es": "^4.17.12",