docs(examples): add builder-adversary-stateless — context-lean variant

Same pattern + AI-as-adversary verification as builder-adversary-min, but the
role prompts add CONTEXT HYGIENE: /compact at every checkpoint (lossless — state
is on disk), read diffs not trees, spill bulk output to files, adversary loads
only {plan, STATUS, diff}. Loop agents non-resumed → fresh session per phase.
Targets cache-read (the dominant cost in a long loop) without changing what the
agents do or how they verify.

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

examples/builder-adversary-stateless/prompts/kickoff.md

@@ -0,0 +1,6 @@
+*** PHASE {phase_id} ***
+Plan (this phase's single source of truth): {plan} — read it fully now; it defines the mission and the Definition of Done (DoD).
+Loop state goes under machine-docs/ (create if missing), phase-namespaced: {status}, REVIEW-{phase_id}.md, JOURNAL-{phase_id}.md, BACKLOG-{phase_id}.md. Never at the repo root.
+Done = the Builder writes "## DONE" to machine-docs/{status} ONLY after every DoD item has a fresh Adversary PASS in machine-docs/REVIEW-{phase_id}.md.
+
+=== role ===