feat(causal): ledger-audit output in the pipeline demo and attrib probe

- causal_pipeline: SMARM_CAUSAL_AUDIT=1 appends render_ledger_audit()
  after the summary; pinned summary format untouched.
- causal_attrib_probe: per-pct audit line (absorbed/forgiven/drops/
  discards) under the existing eff line, so in-site-vs-attributed and
  the loss buckets land in one place for the sweep.

1-core smoke (work + wide): books balance — absorbed = 2x injected and
forgiven = 2x injected, i.e. owed = injected x (N-1) with N=5 actors,
zero outstanding. drop park = 0 even in wide mode (the bottleneck's
queue is never empty, so its in-guard recv never parks); drop yield is
~1500 events but ~0.1ms per window, confirming slice-expiry yields
sample at their own checkpoint. Deficit decomposition needs the
parallel box.

.gitignore

@@ -4,3 +4,4 @@ smarm_trace.json
 /bench_results/
 __pycache__/
 *.pyc
+profile.coz