Aggregates the planning artifacts for the 0049 series (umbrella + 0049a..0049k):
- New rule cpp_apps.md (registered in INDEX) — standardize structure, CMake
patterns, app.md frontmatter and sub-repo for C++ apps; points to the
authoritative cpp/PATTERNS.md and cpp/DESIGN_SYSTEM.md.
- Feature flag osint_graph_v1 (disabled until 0049k closes).
- Issue 0049 (umbrella) and sub-issues 0049b..0049k describing the GPU
rendering system, force-layout, types, sources, labels and the final
graph_explorer app integration.
- README updated with the new rows (all pending; 0049a will flip to
completed in the next commit).
