Retire the Crucible container image

Nothing consumes registry.westgate.pw/deployment/crucible: prod.yml no
longer reserves a slot for it and no runtime or recovery path pulls it.
Binaries, wrappers, and the Nix input are the supported ways to run
Crucible. Delete the image workflows (build/publish/test), the
Dockerfile, and the make image target; update docs to match.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/consumer-contract.md

@@ -49,10 +49,10 @@ by `flake.lock`. CI runs the _same_ `crucible <build>` as local dev, inside the
 nix devshell (binary-cache fast). No build container, no token, no CI-only
 pre-steps.
 
-The `registry.westgate.pw/deployment/crucible:<sha>` image is **deployment-only**:
-`prod.yml` pins it so tools travel with the runtime host (`nwn.enable`), a
-disabled placeholder until the NWN stack lands. It is **not** a build tool and no
-build/CI job consumes it.
+The `registry.westgate.pw/deployment/crucible:<sha>` image is **retired**
+(2026-07-17): nothing consumed it, `prod.yml` no longer reserves a slot for
+it, and CI no longer builds or publishes it. Binaries, wrappers, and the Nix
+input are the only supported ways to run Crucible.
 
 ## Determinism