Drop the ALE-Bench benchmark

It was the suite's only Family B task and the only one that bypassed the
compiler: a hand-written task directory with no build.yaml, so it got none of
the build-time validation the other five benchmarks get. Its optimizer was also
unmetered -- no gateway container, raw upstream credentials in main, no model
allow-list -- which is a fair-play hole in a benchmark whose whole point is
controlled measurement. Its sidecar factory had additionally gone stale against
SidecarEvaluationPolicy and would have died at startup.

The nested-backend refactor now supports `evaluation_backend: command`, so a
replacement Family B task can be built through the compiler and get the gateway
for free. examples/harbor-circle-packing carries a worked version of exactly
that shape, verified end to end.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: varunursekar

harness-engineering-bench/README.md

@@ -36,4 +36,3 @@ promote a task set to the top level once it is ready.
 | [SWE-Atlas-QnA baseline](swe-atlas-qna/baseline/) | Codebase investigation agent | Harbor `scale-ai/swe-atlas-qna` | 20% / 40% / 40% |
 | [tau3 baseline](tau3/baseline/) | MCP customer-service agent | Harbor `sierra-research/tau3-bench` | 20% / 40% / 40% |
 | [BrowseComp-Plus baseline](browsecomp-plus/baseline/) | Fixed-corpus deep-research agent | Pinned local Harbor tasks | 20% / 40% / 40% |
-| [ALE-Bench (ahc011)](ale-bench/) | C++ solver program (component, not an agent) | ALE-Bench AHC problem | public / private seeds |