v4-v6 upgrade improvement and warning about file auto backup

bmad/bmm/testarch/knowledge/probability-impact.md

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+# Probability and Impact Scale
+
+- **Probability**
+  - 1 – Unlikely: standard implementation, low uncertainty.
+  - 2 – Possible: edge cases or partial unknowns worth investigation.
+  - 3 – Likely: known issues, new integrations, or high ambiguity.
+- **Impact**
+  - 1 – Minor: cosmetic issues or easy workarounds.
+  - 2 – Degraded: partial feature loss or manual workaround required.
+  - 3 – Critical: blockers, data/security/regulatory exposure.
+- Multiply probability × impact to derive the risk score.
+  - 1–3: document for awareness.
+  - 4–5: monitor closely, plan mitigations.
+  - 6–8: CONCERNS at the gate until mitigations are implemented.
+  - 9: automatic gate FAIL until resolved or formally waived.
+
+_Source: Murat risk model summary._