Add OrbitHub C++ Qt Widgets spec and Codex prompts

docs/OrbitHub_Codex_Build_Prompt_CPP_QtWidgets.md

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+# OrbitHub Codex Build Prompt (Pure C++ / Qt6 Widgets)
+
+You are Codex. You will implement OrbitHub entirely in C++ using Qt6 Widgets.
+
+The previous Python/Shiboken implementation is abandoned.
+
+## Rules
+
+- Use modern CMake
+- Use Qt6 Widgets only
+- Use C++17 or newer
+- Never block the GUI thread
+- Use Git for checkpointing
+- Maintain docs/PROGRESS.md
+
+## Required Git Workflow
+
+Create milestone branches:
+- milestone-0-restart-cpp
+- milestone-1-storage
+
+Make small logical commits.
+
+Tag milestone completions:
+- v0-m0-done
+- v0-m1-done
+
+## Milestone 0 Deliverable
+
+Implement:
+- ProfilesWindow (QMainWindow)
+- SessionWindow (QMainWindow)
+- QTabWidget hosting placeholder QWidget
+- main.cpp wiring
+
+Stop after Milestone 0 is complete and tagged.