feat: reorganize figures directory for architectural compliance

- Reduce src/figures from 34 to 14 files in main directory (59% reduction)
- Create subdirectories: core/ (9 files), interfaces/ (4 files), plot_types/ (4 files), management/ (3 files)
- Maintain FPM build compatibility and 100% test pass rate
- Address directory size limit violations (was 68% over 20-file soft limit)
- Achieve architectural compliance with clear functional organization

Author: krystophny