feat: Phase 8 - Frontend main views (T-026 to T-031)

Implement all main frontend views for the MITRE ATT&CK coverage platform:

- T-026: Dashboard with coverage summary cards and tactic breakdown table

- T-027: Interactive ATT&CK matrix with filtering by status, tactic, platform

- T-028: Technique detail page with tests, intel items, and review actions

- T-029: Test creation form with technique selector and validation

- T-030: Test detail page with drag and drop evidence upload and download

- T-031: System admin panel with MITRE sync and intel scan controls

New components: CoverageSummaryCard, TacticCoverageChart, AttackMatrix, TechniqueCell, TestForm, EvidenceUpload, EvidenceList

New API modules: metrics.ts, techniques.ts, tests.ts, evidence.ts, system.ts

All views use TanStack Query for data fetching with proper loading and error states. Role-based UI controls for admin/lead actions.

frontend/src/api/system.ts

@@ -0,0 +1,41 @@
+import client from "./client";
+
+export interface SyncMitreResponse {
+  message: string;
+  new: number;
+  updated: number;
+}
+
+export interface IntelScanResponse {
+  message: string;
+  new_items: number;
+}
+
+export interface SchedulerJob {
+  id: string;
+  name: string;
+  next_run_time: string | null;
+}
+
+export interface SchedulerStatusResponse {
+  running: boolean;
+  jobs: SchedulerJob[];
+}
+
+/** Manually trigger MITRE ATT&CK sync. */
+export async function triggerMitreSync(): Promise<SyncMitreResponse> {
+  const { data } = await client.post<SyncMitreResponse>("/system/sync-mitre");
+  return data;
+}
+
+/** Manually trigger threat intelligence scan. */
+export async function triggerIntelScan(): Promise<IntelScanResponse> {
+  const { data } = await client.post<IntelScanResponse>("/system/run-intel-scan");
+  return data;
+}
+
+/** Get scheduler status. */
+export async function getSchedulerStatus(): Promise<SchedulerStatusResponse> {
+  const { data } = await client.get<SchedulerStatusResponse>("/system/scheduler-status");
+  return data;
+}