docs: update all docs for publication
- README.md: new — features, quick start, controls, MCP tools, requirements
- AGENTS.md: rewritten for pure P/Invoke Vulkan 1.3 (was Raylib/OpenGL)
- CORTEX_ENGINE_ARCHITECTURE.md: complete rewrite — current architecture,
frame loop, UBO layout, push constants, shadow mapping, PBR, AI/MCP,
physics, ImGui, video recording, content, testing
- VULKAN_IMPLEMENTATION_PLAN.md: marked as COMPLETE with all 21 phases
- scripts/run.sh: updated examples
- .gitignore: added Videos/, imgui.ini, cortex.mp4
- Removed tracked imgui.ini and video files
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