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

.gitignore

@@ -18,6 +18,12 @@ Thumbs.db
 # Generated screenshots
 Screenshots/
 
+# Video recordings
+Videos/
+
+# ImGui
+imgui.ini
+
 # dotnet
 *.dll
 *.exe
@@ -30,3 +36,4 @@ Screenshots/
 !claude_desktop_config.json
 .playwright-mcp/
 Vulkan-Guide/
+cortex.mp4