fix(review-loop-run): counts parses count-by-severity block with scope + format branches (2026-09-13 fix, 40/40 tests)

Was live via ~/sbin symlink but never committed. Baseline for bug 5352fe72.

Claude-Session: https://claude.ai/code/session_01G3SkMRBRWXyiGuMGs8WVas

tests/fixtures/review-loop-run/heading-numbers.md

@@ -0,0 +1,16 @@
+# Review
+
+## Finding 3 — HTTP 404 on /widgets
+
+### MEDIUM: endpoint returns wrong status
+
+Some prose mentioning 42 and HIGH severity inline that is not a real count.
+
+## Count by severity
+
+| Severity | Count |
+|----------|-------|
+| CRITICAL | 0 |
+| HIGH | 0 |
+| MEDIUM | 1 |
+| LOW | 0 |