Cap C++ compilation builds at -j2

Run C++ compilation as: make -C build/output/linux-clang-debug-make -j2 <target>. Never use -j $(nproc). Non-compilation doc targets (compass build –direct skills/site, or the equivalent cmake deploy_skills target) run directly without a -j cap.

Why: Machine crashed on full-tree make all -j$(nproc): Qt/shared-library link steps are memory-heavy. Emacs-only targets don't compile C++ so they carry no risk.

How to apply: For C++ compilation: always -j2. For compass build –direct skills, the cmake deploy_skills target, etc: run directly, no -j flag.