test(e2e): sprint 3 acceptance tests — US-13 to US-16

Four new spec files covering the MITRE multi-technique feature:
- us13: API contract (techniques array, dedup, unknown ID → 400, SOC 403, auto-transition)
- us14: tag UI (empty state, add/remove auto-save, SimulationList column, order, styling)
- us15: matrix modal (tactic tree, layout, select/expand/search, Apply/Cancel/Escape/backdrop, a11y)
- us16: sprint 2 regression (workflow, badge, SOC RBAC, picker still works)

Updated sprint 2 specs (us8, us10) to use technique_ids array and Quick search button
instead of deprecated scalar mitre_technique_id/name fields.

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

e2e/tests/us8-simulation-redteam-fill.spec.ts

@@ -79,8 +79,7 @@ test.describe('US-8 — redteam fill simulation details', () => {
 
     const patch = {
       name: 'Updated name',
-      mitre_technique_id: 'T1059',
-      mitre_technique_name: 'Command and Scripting Interpreter',
+      technique_ids: ['T1059'],
       description: 'Some description',
       commands: 'cmd /c whoami\ncmd /c ipconfig',
       prerequisites: 'Admin shell',
@@ -90,8 +89,10 @@ test.describe('US-8 — redteam fill simulation details', () => {
     const r = await client.patch(`/simulations/${sim.id}`, patch);
     expect(r.status).toBe(200);
     expect(r.data.name).toBe('Updated name');
-    expect(r.data.mitre_technique_id).toBe('T1059');
-    expect(r.data.mitre_technique_name).toBe('Command and Scripting Interpreter');
+    // sprint 3: techniques array replaces scalar scalars
+    expect(Array.isArray(r.data.techniques)).toBe(true);
+    expect(r.data.techniques[0].id).toBe('T1059');
+    expect(r.data.techniques[0].name).toBe('Command and Scripting Interpreter');
     expect(r.data.description).toBe('Some description');
     expect(r.data.commands).toBe('cmd /c whoami\ncmd /c ipconfig');
     expect(r.data.prerequisites).toBe('Admin shell');
@@ -199,7 +200,7 @@ test.describe('US-8 — redteam fill simulation details', () => {
     await deleteSimulation(redteamToken, sim.id);
   });
 
-  test('AC-8.6 — MITRE technique picker is present on the edit form', async ({
+  test('AC-8.6 — MITRE technique picker accessible via Quick search on the edit form', async ({
     page,
     context,
   }) => {
@@ -208,6 +209,8 @@ test.describe('US-8 — redteam fill simulation details', () => {
     await seedTokenInStorage(context, redteamToken);
     await page.goto(`/engagements/${engagementId}/simulations/${sim.id}/edit`);
 
+    // Sprint 3: picker is inside MitreTechniquesField, opened via "Quick search"
+    await page.getByRole('button', { name: /quick search/i }).click();
     // MitreTechniquePicker renders an input with combobox role
     await expect(page.getByRole('combobox', { name: /mitre technique/i })).toBeVisible();