docs(examples): add a Builder/Adversary loop-pair example (the cc-ci pattern)

A self-contained examples/builder-adversary/ that distills the cc-ci production
loop pair into a tiny, fully-local task (build a `wc` CLI in two phases):

- agents.toml: builder + adversary loops, persistent orchestrator, on_complete
  reporter, cleanlogs service; phase machine with a per-phase model override
- prompts/: kickoff template + builder/adversary roles carrying the load-bearing
  protocol (claim()/review() handoff, machine-docs file-location rule,
  WHAT+HOW+EXPECTED+WHERE=STATUS / WHY=JOURNAL anti-anchoring, WAITING-UNTIL liveness)
- plans/: two phase plans (wc, json) each with a cold-verifiable Definition of Done
- README: how to run, the work-repo two-clone isolation model, how to adapt

Verified: `agents.py status --config agents.toml` parses and lists all agents.

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

examples/builder-adversary/machine-docs/.gitkeep

@@ -0,0 +1,3 @@
+# Coordination / loop-state files live here at runtime (phase-namespaced STATUS / REVIEW / BACKLOG /
+# JOURNAL, shared DECISIONS.md, and the ADVERSARY-INBOX.md / BUILDER-INBOX.md side-channels).
+# This .gitkeep just ensures the directory exists; the loop pair populates it. See ../README.md.