docs(extraction): correct value-refs coverage count in playbook header (7 → 15 done)

The §2b 'Done' header still read '(7 + 3 inherited)' from an earlier stage;
the tracker below it now lists 15 validated languages. Sync the count.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/design/value-reference-edges-playbook.md

@@ -165,7 +165,7 @@ Tracked against the README's **Supported Languages** table (24 rows) and **Frame
 Routes** list. Value-refs is **language-level**, so frameworks are *not* a separate axis (see
 the bottom of this section).
 
-**✅ Done — validated S/M/L (7 + 3 inherited):**
+**✅ Done — validated S/M/L (15 + 3 inherited):**
 
 | Language | How |
 |---|---|