feat(algorithms): add voronoi and delaunay demo

Delaunay uses Bowyer-Watson with an exact in-circle test. Voronoi
cells are its dual, clipped to the canvas. Click adds a point, drag
moves it; layer toggles and an optional step mode. Max 400 points.
ROADMAP: tick Voronoi, drop the Lenia zoom item.

ROADMAP.md

@@ -19,13 +19,12 @@ Open ideas for the playground frontend. Tick a box when done.
 
 ## Features
 
-- [ ] Lenia: display zoom so small creatures (e.g. Orbium bicaudatus tails) are visible
 - [ ] **Shareable demo state**: keep demo settings in query params (fractal zoom/center, sorting algorithm, seeds). Opening the link restores the view.
 - [ ] **New algorithm demos** (pattern: route + `RouterConstants` + `AlgorithmsService` entry + i18n + information panel):
   - [x] Boids / flocking (GPU path like cloth)
   - [x] **Physarum** (slime mold transport networks, trail map on GPU compute, CPU fallback)
   - [ ] Boids 3D (later, 2D done)
-  - [ ] Voronoi / Delaunay
+  - [x] **Voronoi / Delaunay** (Bowyer-Watson, CPU + Canvas 2D)
   - [x] A* vs Dijkstra side by side (reuse pathfinding)
   - [x] Fourier epicycles
   - [x] Reaction-diffusion (Gray-Scott) shader (reuse the fractal shader setup)