fix(backend): sprint 3 post-review — nullable migration + dead code + tactic names

- Migration 0003: enforce techniques NOT NULL via batch_alter_table
- Migration 0003: remove unused _sims table proxy and dead column/table imports
- mitre.py: add _TACTIC_NAMES dict to fix 'Command And Control' → 'Command and Control'

backend/migrations/versions/0003_simulation_techniques_array.py

@@ -8,7 +8,7 @@ import json
 
 from alembic import op
 import sqlalchemy as sa
-from sqlalchemy.sql import column, table, text
+from sqlalchemy.sql import text
 
 
 revision = "0003"
@@ -16,15 +16,6 @@ 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()
@@ -47,8 +38,8 @@ def upgrade():
         )
 
     # 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.
+    with op.batch_alter_table("simulations") as batch_op:
+        batch_op.alter_column("techniques", existing_type=sa.Text(), nullable=False)
 
     # 4. Drop old scalar columns.
     with op.batch_alter_table("simulations") as batch_op: