docs(driver-opcuaclient): correct open-findings count to 2

Driver.OpcUaClient-006, -007, -008, -009, -010, -012, -013, -015 were
resolved in earlier commits; only -011 (Low) and -014 (Low) remain open.
Header was left at 3 after the Medium batch; correct to 2.

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

code-reviews/Driver.OpcUaClient/findings.md

@@ -7,7 +7,7 @@
 | Review date | 2026-05-22 |
 | Commit reviewed | `76d35d1` |
 | Status | Reviewed |
-| Open findings | 3 |
+| Open findings | 2 |
 
 ## Checklist coverage