fix(m4): typed MitreSyncResult interface — drop the as cast

Mirrors the backend Pydantic `SyncResultOut` in TS so the mutation result is
properly typed end-to-end. `(res as { duration_ms: number })` cast removed
from MitrePage.tsx; `apiPost<MitreSyncResult>` carries the contract.

Also annotated the unused query-key factories in mitre.ts so the next reader
knows they're parked for M5 template-form consumption (not dead).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/lib/mitre.ts

@@ -51,6 +51,10 @@ export interface MitreTag {
   name: string;
 }
 
+// Query keys. `status` + `matrix` drive the M4 picker; the per-list factories
+// (`tactics`/`techniques`/`subtechniques`) are unused today but the M5
+// template forms will consume them for the standalone REST endpoints when
+// users edit a single test's tags inline.
 export const mitreKeys = {
   status: ['mitre', 'status'] as const,
   matrix: ['mitre', 'matrix'] as const,
@@ -85,3 +89,17 @@ export interface MatrixTactic {
 export interface MitreMatrix {
   tactics: MatrixTactic[];
 }
+
+/** Mirror of backend `SyncResultOut` (`api/mitre.py`). */
+export interface MitreSyncResult {
+  tactics_upserted: number;
+  techniques_upserted: number;
+  subtechniques_upserted: number;
+  subtechniques_skipped_orphan: number;
+  technique_tactic_links: number;
+  version: string | null;
+  source: string;
+  started_at: string;
+  finished_at: string;
+  duration_ms: number;
+}

frontend/src/pages/MitrePage.tsx

@@ -9,7 +9,12 @@ import { SectionHeader } from '@/components/ui/SectionHeader';
 import { Tag } from '@/components/ui/Tag';
 import { ApiError, apiGet, apiPost } from '@/lib/api';
 import { useAuth } from '@/lib/auth';
-import { mitreKeys, type MitreStatus, type MitreTag } from '@/lib/mitre';
+import {
+  mitreKeys,
+  type MitreStatus,
+  type MitreSyncResult,
+  type MitreTag,
+} from '@/lib/mitre';
 
 export function MitrePage() {
   const { state } = useAuth();
@@ -24,14 +29,14 @@ export function MitrePage() {
   });
 
   const sync = useMutation({
-    mutationFn: () => apiPost<Record<string, unknown>>('/mitre/sync'),
+    mutationFn: () => apiPost<MitreSyncResult>('/mitre/sync'),
     onMutate: () => {
       setSyncResult(null);
       setSyncError(null);
     },
     onSuccess: async (res) => {
       const counts = `${res.tactics_upserted} tactics, ${res.techniques_upserted} techniques, ${res.subtechniques_upserted} subtechniques`;
-      setSyncResult(`Sync completed in ${(res as { duration_ms: number }).duration_ms / 1000}s — ${counts}.`);
+      setSyncResult(`Sync completed in ${(res.duration_ms / 1000).toFixed(1)}s — ${counts}.`);
       await qc.invalidateQueries({ queryKey: ['mitre'] });
     },
     onError: (e) => {