fix BS-3606
#### PR Dependency Tree
* **PR #12892**
* **PR #12895** 👈
This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Introduced support for embedding generic iframes with customizable
dimensions and permissions, while ensuring only secure, non-AFFiNE URLs
are allowed.
* Enhanced embedding options by prioritizing custom embed blocks over
iframe blocks for a richer embedding experience across toolbars and link
actions.
* Added URL validation to support secure and flexible embedding
configurations.
* **Bug Fixes**
* Improved iframe embedding reliability by removing restrictive HTTP
headers and certain Content Security Policy directives that could block
iframe usage in the Electron app.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Closes: [BS-3555](https://linear.app/affine-design/issue/BS-3555/ui-attachment-loading-变量更新)
Closes: [BS-3559](https://linear.app/affine-design/issue/BS-3559/ui-图片-loading-变量更新)
### Dark
<img width="625" alt="Screenshot 2025-05-26 at 20 32 36" src="https://github.com/user-attachments/assets/93501e3d-8fc6-45f9-84a0-ac147e5c5f9f" />
### Light
<img width="623" alt="Screenshot 2025-05-26 at 20 32 25" src="https://github.com/user-attachments/assets/7d5bc128-6667-45b5-982d-dab3a22706a7" />
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Loading icons are now invoked as functions, allowing for more flexible and customizable rendering with parameters like size and progress.
- **Refactor**
- Replaced theme-dependent and static loading icon references with a unified `LoadingIcon()` component across multiple components and blocks.
- Removed legacy icon variants and simplified icon import statements, centralizing icon rendering logic.
- **Style**
- Updated styles for loading and reload buttons to use theme-aware CSS variables.
- Enlarged and repositioned loading indicators in image blocks for better visibility.
- **Bug Fixes**
- Achieved consistent loading icon rendering across various blocks and components by standardizing icon invocation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Introduced a unified loading spinner icon that adapts to light or dark themes automatically.
- **Refactor**
- Streamlined loading icon usage across the app by replacing multiple theme-based icons with a single helper function for consistent and simplified icon management.
- **Chores**
- Removed an unused dependency to improve package management.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Peng Xiao