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/app/services/mitre.py

@@ -26,6 +26,21 @@ _TACTIC_ORDER = [
     "impact",
 ]
 
+_TACTIC_NAMES: dict[str, str] = {
+    "initial-access": "Initial Access",
+    "execution": "Execution",
+    "persistence": "Persistence",
+    "privilege-escalation": "Privilege Escalation",
+    "defense-evasion": "Defense Evasion",
+    "credential-access": "Credential Access",
+    "discovery": "Discovery",
+    "lateral-movement": "Lateral Movement",
+    "collection": "Collection",
+    "command-and-control": "Command and Control",
+    "exfiltration": "Exfiltration",
+    "impact": "Impact",
+}
+
 mitre_loaded: bool = False
 _index: list[dict[str, Any]] = []
 _tactics_by_technique: dict[str, list[str]] = {}
@@ -87,7 +102,7 @@ def _build_matrix(entries: list[dict[str, Any]]) -> list[dict[str, Any]]:
         techs = tactic_techs.get(tactic_id, [])
         # Sort techniques alphabetically.
         techs_sorted = sorted(techs, key=lambda x: x["name"])
-        tactic_name = tactic_id.replace("-", " ").title()
+        tactic_name = _TACTIC_NAMES.get(tactic_id, tactic_id.replace("-", " ").title())
         matrix.append(
             {
                 "tactic_id": tactic_id,

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: