feat(backend): sprint 3 — multi-technique simulations + MITRE matrix

- Simulation model: replace mitre_technique_id/name scalars with techniques JSON column [{id, name}]
- Alembic migration 0003: add techniques, backfill from scalars, drop old columns (reversible)
- MITRE service: add get_tactics(), lookup_name(), get_matrix() with canonical tactic order and sub-technique nesting
- serializer: enrich techniques with tactics from service at serialize time (graceful empty tactics if bundle outdated)
- simulation_workflow: PATCH now accepts technique_ids list, validates against bundle, deduplicates preserving order, auto-transitions on non-empty list
- simulations API: add GET /api/mitre/matrix endpoint (503 if bundle absent)
- test_mitre.py: updated _reset_mitre fixture, added T1059.006 sub-technique, 14 new tests for get_tactics/lookup_name/get_matrix/matrix endpoint
- test_simulations_techniques.py: 20 new tests covering AC-13.1 to AC-13.5 (create, PATCH, dedup, auto-transition, SOC blocked, migration backfill logic)

Total: 161 tests passing. ruff clean. mypy: no new errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/versions/0003_simulation_techniques_array.py

@@ -0,0 +1,82 @@
+"""replace scalar MITRE columns with techniques JSON array
+
+Revision ID: 0003
+Revises: 0002
+Create Date: 2026-05-27 00:00:00.000000
+"""
+import json
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.sql import column, table, text
+
+
+revision = "0003"
+down_revision = "0002"
+branch_labels = None
+depends_on = None
+
+# Lightweight table proxies for data migration (no ORM import).
+_sims = table(
+    "simulations",
+    column("id", sa.Integer),
+    column("mitre_technique_id", sa.String),
+    column("mitre_technique_name", sa.String),
+    column("techniques", sa.Text),
+)
+
+
+def upgrade():
+    bind = op.get_bind()
+
+    # 1. Add techniques column (nullable while we backfill).
+    op.add_column("simulations", sa.Column("techniques", sa.Text(), nullable=True))
+
+    # 2. Backfill: scalar → JSON array.
+    rows = bind.execute(
+        text("SELECT id, mitre_technique_id, mitre_technique_name FROM simulations")
+    ).fetchall()
+    for row in rows:
+        if row[1]:  # mitre_technique_id is not null
+            val = json.dumps([{"id": row[1], "name": row[2] or ""}])
+        else:
+            val = "[]"
+        bind.execute(
+            text("UPDATE simulations SET techniques = :v WHERE id = :id"),
+            {"v": val, "id": row[0]},
+        )
+
+    # 3. Make NOT NULL now that every row has a value.
+    # SQLite doesn't support ALTER COLUMN, so we skip the nullable constraint
+    # change at DDL level — the application model enforces it.
+
+    # 4. Drop old scalar columns.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.drop_column("mitre_technique_id")
+        batch_op.drop_column("mitre_technique_name")
+
+
+def downgrade():
+    bind = op.get_bind()
+
+    # 1. Re-add scalar columns.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.add_column(sa.Column("mitre_technique_id", sa.String(length=32), nullable=True))
+        batch_op.add_column(sa.Column("mitre_technique_name", sa.String(length=255), nullable=True))
+
+    # 2. Back-fill: take first element of techniques array.
+    rows = bind.execute(text("SELECT id, techniques FROM simulations")).fetchall()
+    for row in rows:
+        techniques = json.loads(row[1] or "[]")
+        if techniques:
+            first = techniques[0]
+            bind.execute(
+                text(
+                    "UPDATE simulations SET mitre_technique_id = :tid, mitre_technique_name = :tname WHERE id = :id"
+                ),
+                {"tid": first.get("id"), "tname": first.get("name"), "id": row[0]},
+            )
+
+    # 3. Drop techniques column.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.drop_column("techniques")