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.

examples/causal_pipeline.rs

@@ -247,6 +247,12 @@ fn main() {
         background.join().unwrap();
 
         print!("{}", smarm::causal::render_summary(&results));
+        // RFC 007 deficit hunt: SMARM_CAUSAL_AUDIT=1 appends the per-cell
+        // ledger audit (injected/absorbed/forgiven + drop and discard
+        // buckets) without touching the pinned summary format.
+        if std::env::var_os("SMARM_CAUSAL_AUDIT").is_some() {
+            print!("{}", smarm::causal::render_ledger_audit(&results));
+        }
         let coz = smarm::causal::render_coz(&results);
         match std::fs::write("profile.coz", coz) {
             Ok(()) => println!("\nwrote profile.coz"),