add Android and Windows clients

[Aidenwu0209]

Summary

• Add a native Android client under android/CodexFlowAndroid with dashboard, session detail, approvals, settings, API client, SSE refresh, and unit tests.
• Add a WinUI 3 Windows client under windows/CodexFlowWindows with dashboard, session detail, approvals, settings, API/SSE clients, and xUnit tests.
• Add a shared client API contract and update project docs to describe the iOS, Android, and Windows client matrix.
• Harden approval resolution in the Mac Agent so pending approvals are not lost when payload decoding or JSON-RPC reply fails.

Why

CodexFlow now has Android and Windows clients that consume the same Mac Agent HTTP API and SSE event stream instead of speaking raw Codex protocol or controlling a terminal. The shared contract keeps the client implementations aligned across platforms.

The approval handling fix came from integration review: previously a pending approval could be removed from local state before the reply to Codex succeeded. This PR restores the pending approval on reply failure and avoids removing it when the payload is invalid.

Validation

• go test ./...
• ./gradlew testDebugUnitTest assembleDebug
• ./gradlew lintDebug
• git diff --check

Notes

• Windows build/tests were not executed locally because the current macOS environment does not have dotnet or msbuild installed.
• Android emulator UI QA was not executed because no adb device was connected.

[hebicheng]

已经使用flutter实现多端了，谢谢兄弟的 contribution～