feat(api): add dashboard summary endpoint (#459)

Create GET /api/dashboard/summary aggregating 10 parallel Prisma
queries: task metrics, active agents, project counts, error rate,
recent activity, active runner jobs with steps, token budget entries.

Guarded by AuthGuard + WorkspaceGuard + PermissionGuard.
Includes DTO classes and unit tests.

Task: MS-P2-001

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

apps/api/src/dashboard/dto/dashboard-summary.dto.ts

@@ -0,0 +1,53 @@
+/**
+ * Dashboard Summary DTO
+ * Defines the response shape for the dashboard summary endpoint.
+ */
+
+export class DashboardMetricsDto {
+  activeAgents!: number;
+  tasksCompleted!: number;
+  totalTasks!: number;
+  tasksInProgress!: number;
+  activeProjects!: number;
+  errorRate!: number;
+}
+
+export class RecentActivityDto {
+  id!: string;
+  action!: string;
+  entityType!: string;
+  entityId!: string;
+  details!: unknown;
+  userId!: string;
+  createdAt!: string;
+}
+
+export class ActiveJobStepDto {
+  id!: string;
+  name!: string;
+  status!: string;
+  phase!: string;
+}
+
+export class ActiveJobDto {
+  id!: string;
+  type!: string;
+  status!: string;
+  progressPercent!: number;
+  createdAt!: string;
+  updatedAt!: string;
+  steps!: ActiveJobStepDto[];
+}
+
+export class TokenBudgetEntryDto {
+  model!: string;
+  used!: number;
+  limit!: number;
+}
+
+export class DashboardSummaryDto {
+  metrics!: DashboardMetricsDto;
+  recentActivity!: RecentActivityDto[];
+  activeJobs!: ActiveJobDto[];
+  tokenBudget!: TokenBudgetEntryDto[];
+}