feat(lenia): add lenia demo and shared gpu-state module

Move gpu-state.ts out of gray-scott so gray-scott and lenia share it.
Fix gray-scott: skip the texture swap until the step shader is ready,
otherwise the seed is lost.
Info panel: support routerLink, so GoL and Lenia link to each other.

ROADMAP.md

@@ -28,4 +28,5 @@ 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] **Lenia** (continuous Game of Life, shader ping-pong like Gray-Scott)
   - [x] **Ant colony** (ACO on TSP, CPU + Canvas 2D)