docs(examples): add builder-adversary-min — minimal-prompt variant

Same topology/behaviour as builder-adversary (loop pair, phase machine,
claim()/review() handoff, machine-docs coordination, cold verification) but the
role + kickoff prompts are compressed to minimal tokens, keeping every
load-bearing rule. Config and plans are unchanged. The separate
agent-orchestrator-benchmark repo runs a head-to-head token comparison.

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

examples/builder-adversary-min/README.md

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+# Builder/Adversary example — minimal-prompt variant
+
+Same as [`../builder-adversary`](../builder-adversary/) in every way that matters — Builder +
+Adversary loop pair, phase machine, `claim(`/`review(` git handoff, `machine-docs/` coordination,
+cold verification — but the **role + kickoff prompts are compressed to minimal tokens**, keeping
+every load-bearing rule (the commit-prefix handoff, the `machine-docs/` file rule, the
+`WHAT+HOW+EXPECTED+WHERE=STATUS / WHY=JOURNAL` anti-anchoring contract, and the `WAITING-UNTIL`
+liveness protocol).
+
+Why: the prompts are sent to the agents on every kickoff, so trimming them trims tokens. Config and
+plans are unchanged from the original (they aren't part of the prompt). See the original's README for
+the full explanation of the pattern, how to run it, and the work-repo isolation model — the commands
+are identical, just `--config` this directory's `agents.toml`.
+
+```bash
+python3 ../../agents.py status --config agents.toml
+python3 ../../agents.py up     --config agents.toml      # needs `claude` on PATH
+```
+
+## How small?
+
+`prompts/builder.md` and `prompts/adversary.md` here are roughly **half to a third** the size of the
+originals, with the same rules stated tersely. The separate **`agent-orchestrator-benchmark`** repo
+runs a head-to-head: the same task built independently by this variant and the original (both on
+Sonnet), with token counts for each — confirming the minimal prompts still get the job done and
+quantifying the savings.