Feature Request: Add official OpenHarmony platform support

### Summary

Dioxus currently does not support the OpenHarmony operating system. I would like to request official platform integration for OpenHarmony to enable cross-platform Dioxus application development on this ecosystem.

### Use Case & Background

OpenHarmony is a fast-growing open-source distributed operating system widely used in mobile, IoT, embedded, education and industrial devices. Many Rust and cross-platform developers in China are building applications targeting OpenHarmony devices.

As Dioxus already supports Android, iOS, Web, Desktop and other mainstream platforms, adding OpenHarmony support will expand Dioxus's reach into the OpenHarmony ecosystem, attracting more developers to adopt the framework.

### Expected Requirements

1. Add OpenHarmony target compilation support for Rust toolchain
2. Implement platform-specific window/render layer adapter for OpenHarmony native ArkUI runtime
3. Provide official OpenHarmony build toolchain & dx bundle support
4. Add OpenHarmony example projects to the repo
5. Document porting & deployment workflow in official docs

### Additional Info

- OpenHarmony uses RISC-V/ARM architectures with native Rust compilation support
- The ecosystem has official Rust NDK and native component APIs
- I am available to assist with early porting research, testing and sample validation if the team plans to implement this feature.

### Labels Suggestion

enhancement, new-platform, cross-platform, ecosystem

No files, tests, or entry points are named. Start by surveying the existing Android, iOS, desktop, and dx platform integrations, then investigate Rust target support and OpenHarmony's ArkUI and build tooling. Done would require the target, native adapter, dx bundle support, examples, and deployment documentation listed in the issue.

Written by the indexing model from the issue text.