feat(ant-colony): add ant colony optimization demo for tsp

Ant System on the travelling salesman problem, run on the CPU.
Click the canvas to add cities while the colony runs.
Show the nearest-neighbor tour as a baseline. Tick ROADMAP.

ROADMAP.md

@@ -28,3 +28,4 @@ Open ideas for the playground frontend. Tick a box when done.
   - [x] A* vs Dijkstra side by side (reuse pathfinding)
   - [x] Fourier epicycles
   - [x] Reaction-diffusion (Gray-Scott) shader (reuse the fractal shader setup)
+  - [x] **Ant colony** (ACO on TSP, CPU + Canvas 2D)