Retire the Crucible container image (#41)

## Summary

The `registry.westgate.pw/deployment/crucible` image has no consumer: `prod.yml` no longer reserves a slot for it (contract settled in sow-platform PR #64) and no runtime or recovery path pulls it. Binaries, wrappers, and the Nix input remain the supported ways to run Crucible.

## What changed

- Deleted `.gitea/workflows/build-image.yml`, `publish-image.yml`, `test-image.yml`
- Deleted `docker/Dockerfile` and the `make image` target
- Updated README, AGENTS.md, and `docs/consumer-contract.md` to state the image is retired

Existing `deployment/crucible` images in the registry can be deleted at leisure; nothing references them.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #41
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

README.md

@@ -71,10 +71,9 @@ nix develop            # Go + shellcheck + yamllint + make
 make check             # go vet + go test + shellcheck + yamllint
 make build             # build every cmd/* into ./bin (gitignored)
 make smoke             # build + assert the fail-closed contract
-make image             # docker build -> crucible:<sha>
 ```
 
-Binaries are **never committed** — they are CI artifacts / image layers (D19).
+Binaries are **never committed** — they are CI artifacts (D19).
 This retires the old habit of checking in `nwn-tool` / `sow-toolkit`.
 
 ## CI
@@ -84,12 +83,8 @@ publish event is a `v*` tag (see `runbooks/ci-trigger-standard.md` in sow-docs,
 https://git.westgate.pw/ShadowsOverWestgate/sow-docs).
 
 - `test.yml` — vet, test, shellcheck, yamllint, binary smoke (PR + main).
-- `test-image.yml` — build the OCI image to prove it compiles (PR + main, no push).
 - `build-binaries.yml` — cross-build all targets (PR + main); on a `v*` tag, upload
   the binaries, `SHA256SUMS`, and the wrappers to the Gitea release.
-- `build-image.yml` — on a `v*` tag, build and publish
-  `registry.westgate.pw/deployment/crucible:<sha>`.
-- `publish-image.yml` — manual `workflow_dispatch` break-glass republish.
 - `sync-wrappers.yml` — on a `main` push that touches `wrappers/`, auto-PR the
   canonical wrappers to the consumer repos in `wrappers/consumers.txt`.
   Consumer drift checks run after those PRs merge to `main`, not on the PRs