Add observable AppConfig (grid/snap/arc-on-crossing/animation/theme),
pure-geometry orthogonal router with grid-snapped bends and perpendicular
crossing detection for arc hops, and a mock flow-distribution solver that
pushes supply to demand along shortest paths and records signed per-edge
flow and direction. Covered by routing and flow-solver tests.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
