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,