docs: [#428] record mysql remediation decision and validation

- evaluated candidate tags; no safer easy upgrade selected

- validated mysql:8.4 runtime behavior

Author: josecelano

docs/issues/428-docker-vulnerability-analysis-apr8-2026.md

@@ -123,8 +123,8 @@ For each image, execute these steps in order:
 #### 8. MySQL (`mysql:8.4`)
 
 - [x] Analysis and triage completed
-- [ ] Easy remediation implemented (if available)
-- [ ] Image rebuilt and validated
+- [x] Easy remediation implemented (if available; no safe tag improvement found)
+- [x] Image rebuilt and validated
 - [ ] Trivy re-scan completed and compared
 - [ ] Scan docs updated
 - [ ] Follow-up issue created (only if unresolved)