♻️ remove ShannonLoss, add domain-specific loss types (ConvergenceLoss, RoutingLoss)

ShannonLoss was a generic information-theoretic placeholder. Replace with
three domain-specific loss types that carry semantic meaning:

- ConvergenceLoss: distance to crystal (steps remaining, combine = max)
- ApertureLoss: redesigned with aperture fraction field (combine = union + max)
- RoutingLoss: decision uncertainty (entropy + runner-up gap, combine = max)

Imperfect<T, E, L> no longer has a default type parameter — callers must
choose their loss type explicitly. 74 tests pass.

Author: Mara

flake.lock

@@ -4,7 +4,7 @@
   inputs = {
     nixpkgs.url     = "github:NixOS/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
-    flakes.url      = "path:/Users/alexwolf/.flakes";
+    flakes.url      = "github:systemic-engineering/flakes";
     flakes.inputs.nixpkgs.follows = "nixpkgs";
     flakes.inputs.flake-utils.follows = "flake-utils";
   };