feat(physarum): add slime mold network demo

Add a Physarum route with a GPU trail map and a CPU fallback.
Tick the Physarum item in ROADMAP.md.

src/app/constants/RouterConstants.ts

@@ -60,6 +60,11 @@
     LINK: '/algorithms/boids',
   };
 
+  static readonly PHYSARUM = {
+    PATH: 'algorithms/physarum',
+    LINK: '/algorithms/physarum',
+  };
+
   static readonly FOUR_COLOR = {
     PATH: 'algorithms/four_color',
     LINK: '/algorithms/four_color',