v0.1.5 — survive list-shaped distill responses; robustness tier complete

• ingest/_json: a distill response whose first parseable JSON value is a
  list no longer crashes remember() ('list' object has no attribute 'get'). extract_json now prefers the first JSON object — skipping prose
  debris like a stray [] before the real payload — and returns a bare array
  only as a fallback, which ingest normalizes as the triples payload with its
  wrapper omitted. Found by the robustness tier's first lmsys-chat-1m run
  (3/368 real turns crashed, all code-shaped inputs).
• tests: robustness tier Phase 2 — S4 (reinforcement ≠ duplication: a seeded
  sample of fact-yielding turns is re-ingested; new-edge growth is reported as a
  distribution) and S5 (every maintain() report must carry non-negative counts
  bounded by the store it ran over). Both soft signals; hard gates unchanged.