feat(frontend): sprint 4 — dark mode + matrix overhaul + tactic selection + done read-only + UI polish

US-17: fix duplicate "Create engagement" button, icon conventions (Save/RotateCcw/Grid2x2), UsersAdminPage form baseline alignment
US-18: done status fully read-only + Reopen button (done → review_required) for all roles
US-19: invalidate engagement queries on simulation PATCH/transition for auto-status propagation
US-20: MitreMatrixModal rewritten — CSS grid 12-column layout, no horizontal scroll, attack.mitre.org compact look
US-21: tactic header clickable in matrix, tactic chips (MitreTacticTag) in field, single atomic PATCH with technique_ids + tactic_ids
US-22: MitreTechniquesField chips-only area + inline search input + matrix icon button; chips show ID-only (name in title=)
US-23: useTheme hook — 3-state light/dark/system, CSS variables, Tailwind darkMode class, localStorage persistence

92/92 tests passing, typecheck and lint clean.

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

frontend/src/api/types.ts

@@ -78,11 +78,17 @@ export interface MitreTactic {
   techniques: MitreMatrixTechnique[];
 }
 
+export interface MitreTacticRef {
+  id: string;
+  name: string;
+}
+
 export interface Simulation {
   id: number;
   engagement_id: number;
   name: string;
   techniques: MitreTechnique[];
+  tactics: MitreTacticRef[];
   description: string | null;
   commands: string | null;
   prerequisites: string | null;
@@ -105,6 +111,7 @@ export interface SimulationCreateInput {
 export interface SimulationPatchInput {
   name?: string;
   technique_ids?: string[];
+  tactic_ids?: string[];
   description?: string | null;
   commands?: string | null;
   prerequisites?: string | null;