Add risks_mitigations table

Signed-off-by: gearnode <bryan@frimin.fr>

pkg/coredata/migrations/20250401T080600Z.sql

@@ -0,0 +1,7 @@
+CREATE TABLE risks_mitigations (
+    risk_id TEXT NOT NULL REFERENCES risks(id),
+    mitigation_id TEXT NOT NULL REFERENCES mitigations(id),
+    probability float NOT NULL,
+    impact float NOT NULL,
+    PRIMARY KEY (risk_id, mitigation_id)
+);