feat(techniques): add external_references storage and display MITRE sources with links

backend/alembic/versions/b049_add_technique_external_references.py

@@ -0,0 +1,26 @@
+"""Add external_references column to techniques table.
+
+Revision ID: b049
+Revises: b048
+Create Date: 2026-06-18
+"""
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import JSONB
+
+revision = "b049"
+down_revision = "b048"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "techniques",
+        sa.Column("external_references", JSONB, nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("techniques", "external_references")