add claude.md file with basic engine understanding

[Ikreb1]

I think this is a minimum required for the agents to read and understand the engine better but it can be hard to tell if this is a net positive

[Copilot]

Pull request overview

Adds a new top-level CLAUDE.md to provide coding agents and new developers with a concise orientation to the Carbon Trinity rendering engine repo, including layout, build workflows, Python/Blue exposure considerations, and common “gotchas”.

Changes:

• Introduces CLAUDE.md with repository structure and naming conventions.
• Documents recommended build presets/targets and common build “tripwires”.
• Describes the Blue exposure layer and practical verification expectations.

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