Correct Firm A framing: replication-dominated, not pure

Interview evidence from multiple Firm A accountants confirms that MOST
use replication (stamping / firm-level e-signing) but a MINORITY may
still hand-sign. Firm A is therefore a "replication-dominated" population,
not a "pure" one. This framing is consistent with:

- 92.5% of Firm A signatures exceed cosine 0.95 (majority replication)
- The long left tail (~7%) captures the minority hand-signers, not scan
  noise or preprocessing artifacts
- Hartigan dip test: Firm A cosine unimodal long-tail (p=0.17)
- Accountant-level GMM: of 180 Firm A accountants, 139 cluster in C1
  (high-replication) and 32 in C2 (middle band = minority hand-signers)

Updates docstrings and report text in Scripts 15, 16, 18, 19 to match.
Partner v3's "near-universal non-hand-signing" language corrected.

Script 19 regenerated with the updated text.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

signature_analysis/15_hartigan_dip_test.py

@@ -10,6 +10,17 @@ Purpose:
   Prior finding (2026-04-16): signature-level distribution is unimodal long-tail;
   the story is that bimodality only emerges at the accountant level.
 
+Firm A framing (2026-04-20, corrected):
+  Interviews with multiple Firm A accountants confirm that MOST use
+  replication (stamping / firm-level e-signing) but do NOT exclude a
+  minority of hand-signers. Firm A is therefore a "replication-dominated"
+  population, NOT a "pure" one. This framing is consistent with:
+    - 92.5% of Firm A signatures exceed cosine 0.95
+    - The long left tail (7.5% below 0.95) captures the minority
+      hand-signers, not scan noise
+    - Script 18: of 180 Firm A accountants, 139 cluster in C1
+      (high-replication) and 32 in C2 (middle band = minority hand-signers)
+
 Tests:
   1. Firm A (Deloitte) cosine max-similarity       -> expected UNIMODAL
   2. Firm A (Deloitte) independent min dHash       -> expected UNIMODAL