Upgrade Flutter SDK to the latest stable version

### Describe your improvement idea or feature request

The project is currently using an older Flutter SDK version (3.29.2), which may lead to compatibility issues with newer dependencies, tooling, and platform updates.

I would like to propose upgrading the Flutter SDK to a more recent stable version(3.38.5) to ensure better performance, improved tooling support, and long-term maintainability of the project.

### How would you like to see it implemented?

1. Upgrade the project to the latest stable Flutter SDK
2. Update the Flutter version constraint and related configuration files
3. Resolve any breaking changes, deprecations, or analyzer warnings
4. Update dependencies only where required for compatibility
5. Verify the app builds and runs correctly across supported platforms
6. Ensure existing functionality remains unchanged
7. Update documentation (e.g., README) to reflect the new Flutter version
8. Update workflows with new flutter version

### Put here any screenshots or videos (optional)

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### How can we contact you (optional)

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### Would you like to work on this issue?

None

### By submitting this issue, I have confirmed that:

- [x] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

首先定位 issue 中提到的 Flutter 版本约束、相关配置文件、workflow 定义和 README 引用。升级 SDK，并仅处理 analyzer 和 build 结果所要求的兼容性变更。验证受支持平台的构建和现有功能，然后确认文档和 workflow 显示新版本。

由索引模型根据 Issue 内容生成。