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/no-count-block.md

@@ -0,0 +1,15 @@
+# Review
+
+### CRITICAL: auth bypass on /admin
+
+Detailed explanation of the bypass.
+
+### HIGH: missing input validation
+
+Detailed explanation.
+
+### HIGH: race condition in worker pool
+
+Detailed explanation.
+
+No explicit count-by-severity section is present in this file.