feat: add perles to CI binary cache

Extract shared package definition, add to flake packages output
and CI workflow so perles gets built and cached by Harmonia.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

flake.nix

@@ -296,6 +296,11 @@
           src = inputs.gastown;
           version = "unstable-${gastownRev}";
         };
+        "custom-perles" = pkgs.callPackage ./packages/perles {
+          inherit (pkgs.unstable) buildGoModule;
+          src = inputs.perles;
+          version = "unstable-${builtins.substring 0 8 (inputs.perles.rev or "unknown")}";
+        };
       } // (if system == "x86_64-linux" then {
         # nix-deck kernel from Jovian-NixOS (Steam Deck) - expensive to build
         "nix-deck-kernel" = self.nixosConfigurations.nix-deck.config.boot.kernelPackages.kernel;