feat(agents): add slice skill

modules/agents/skills.nix

@@ -12,13 +12,14 @@ let
   # The skills installed globally, as derivations from the skills flake.
   # grill interviews the operator relentlessly to resolve a plan before building.
   # design-skill drafts and audits Agent Skills for structural predictability.
-  # wayfinder, research, and prototype guide work from exploration through validation.
+  # wayfinder, research, prototype, and slice guide work from exploration through implementation tickets.
   skills = with inputs.skills.packages.${pkgs.stdenv.hostPlatform.system}; [
     grill
     design-skill
     wayfinder
     research
     prototype
+    slice
   ];
 in
 {