feat(frontend): sprint 3 — multi-technique MITRE selection + matrix modal

- types: replace mitre_technique_id/name scalars with techniques:MitreTechnique[]
  on Simulation; add MitreTactic/MitreMatrixTechnique/MitreMatrixSubtechnique;
  SimulationPatchInput now uses technique_ids:string[]
- api/mitre.ts: add getMitreMatrix() → GET /api/mitre/matrix
- hooks/useMitre: add useMitreMatrix(enabled) with staleTime:Infinity
- MitreTechniquePicker: clean rewrite — onSelect(technique) one-shot, resets
  input after selection, no incoming value props
- MitreTechniqueTag: chip component with id+name and × remove button
- MitreMatrixModal: tactic columns (220px fixed), expand/collapse subtechniques,
  search filter (auto-expands parent on sub match), selection state, focus trap
  (Tab wrap, Escape, search autofocus), backdrop click cancel, Apply N techniques
- MitreTechniquesField: orchestrates tags+picker+matrix with auto-save PATCH on
  every add/remove/Apply, dedup guard, disabled read-only mode for SOC
- SimulationFormPage: swap MitreTechniquePicker for MitreTechniquesField; remove
  technique state from RT form (techniques have independent auto-save cycle)
- SimulationList: MITRE column → T1059 +2 counter format, — when empty
- Tests: 84 passing (13 test files); new suites for Tag, Field, Modal;
  MitreTechniquePicker + SimulationFormPage + SimulationList adapted to new API

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/api/mitre.ts

@@ -1,5 +1,5 @@
 import { apiClient } from './client';
-import type { MitreTechnique } from './types';
+import type { MitreTactic, MitreTechnique } from './types';
 
 export async function searchMitreTechniques(query: string): Promise<MitreTechnique[]> {
   const { data } = await apiClient.get<MitreTechnique[]>('/mitre/techniques', {
@@ -7,3 +7,8 @@ export async function searchMitreTechniques(query: string): Promise<MitreTechniq
   });
   return data;
 }
+
+export async function getMitreMatrix(): Promise<MitreTactic[]> {
+  const { data } = await apiClient.get<MitreTactic[]>('/mitre/matrix');
+  return data;
+}

frontend/src/api/types.ts

@@ -61,12 +61,28 @@ export interface MitreTechnique {
   tactics: string[];
 }
 
+export interface MitreMatrixSubtechnique {
+  id: string;
+  name: string;
+}
+
+export interface MitreMatrixTechnique {
+  id: string;
+  name: string;
+  subtechniques: MitreMatrixSubtechnique[];
+}
+
+export interface MitreTactic {
+  tactic_id: string;
+  tactic_name: string;
+  techniques: MitreMatrixTechnique[];
+}
+
 export interface Simulation {
   id: number;
   engagement_id: number;
   name: string;
-  mitre_technique_id: string | null;
-  mitre_technique_name: string | null;
+  techniques: MitreTechnique[];
   description: string | null;
   commands: string | null;
   prerequisites: string | null;
@@ -88,8 +104,7 @@ export interface SimulationCreateInput {
 
 export interface SimulationPatchInput {
   name?: string;
-  mitre_technique_id?: string | null;
-  mitre_technique_name?: string | null;
+  technique_ids?: string[];
   description?: string | null;
   commands?: string | null;
   prerequisites?: string | null;