docs(examples): add builder-solo — single builder, no adversary (control)

A single Builder that builds AND self-verifies (same DoD rigor), with NO
independent Adversary and no claim/review handoff. The control for measuring
what the AI adversary costs (its tokens, ~half of a loop-pair run) and buys
(independent cold verification vs self-certification).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/builder-solo/README.md

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+# Builder-solo example — no Adversary (self-verification baseline)
+
+A single **Builder** agent, same task spec as [`../builder-adversary`](../builder-adversary/), but
+with **no Adversary**: the Builder builds *and* verifies its own work, then self-certifies `## DONE`.
+No `claim(`/`review(` handoff — there's nothing to hand off to.
+
+This is the **control** for the AI-as-adversary design. Comparing it against `builder-adversary` on
+the same task answers two things:
+
+- **Cost:** how much of a run's tokens is the independent Adversary? (In the loop-pair runs the
+  Adversary is ~45–53% of the total — this variant removes that.)
+- **Quality:** does an independent cold verifier catch things a self-checking builder misses? Self-
+  certification has an obvious failure mode — the same agent that wrote the bug decides whether it's
+  a bug. This variant measures what you give up by dropping the second pair of eyes.
+
+The Builder's role prompt keeps the same verification *rigor* (run every DoD check, try to break it,
+paste observed output, no self-rubber-stamping) — the only thing removed is the **independent**
+adversary. So the comparison is "independent verification vs self-verification," not "verification vs
+none."
+
+```bash
+python3 ../../agents.py status --config agents.toml
+python3 ../../agents.py up     --config agents.toml      # needs `claude` on PATH
+```
+
+The `agent-orchestrator-benchmark` repo runs this head-to-head with the other variants on the same
+multi-phase task and reports tokens + the efficiency ratios.