Switch scene FUnityManager to new project on creation

[oco777]

Summary

• update project creation window to set the active FUnityManager project to the newly created project data
• record undo and mark manager dirty so the change can be reverted and saved

Testing

• not run

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Assignment uses undefined FUnityManager.Project property

The new undo block assigns manager.Project = projectData, but FUnityManager exposes only the ProjectData getter and the editor-only Editor_SetProjectData(...) helper in Runtime/Core/FUnityManager.cs and has no writable Project member. This code will not compile in the editor assembly, blocking the entire project build until the assignment is rewritten to use the available API.

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