First step of mitigation migration

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

pkg/coredata/migrations/20250327T122105Z.sql

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+-- Add organization_id column to mitigations table
+ALTER TABLE mitigations ADD COLUMN organization_id TEXT;
+
+-- Update mitigations to set organization_id based on framework's organization_id
+UPDATE mitigations m
+SET organization_id = f.organization_id
+FROM frameworks f
+WHERE m.framework_id = f.id;
+
+-- Make organization_id NOT NULL after update
+ALTER TABLE mitigations ALTER COLUMN organization_id SET NOT NULL;
+
+-- Add foreign key constraint
+ALTER TABLE mitigations ADD CONSTRAINT fk_mitigations_organization_id
+    FOREIGN KEY (organization_id) REFERENCES organizations(id) ON DELETE CASCADE;
+
+-- Add index for performance
+CREATE INDEX idx_mitigations_organization_id ON mitigations(organization_id);