Adds add_subdirectory block for apps/kanban_cpp (lives in apps/ per issue
0096). The app itself is a sub-repo (gitignored via apps/*/), with its own
git history and master branch initialized.
Six panels reuse registry: http_request_cpp_core, kpi_card_cpp_viz,
sparkline_cpp_viz, agent_runs_timeline_cpp_viz, dod_evidence_panel_cpp_viz.
Backend Go on :8403 (independent operations.db from kanban_web).
Egutierrez