fix: remediate dashboard API integration review blockers (#459)

- Fix race condition: guard useEffect when workspaceId is null, prevent
  infinite loading state by setting isLoading=false on null workspace
- Fix TypeScript strict typing: @Workspace() returns string|undefined,
  controller now matches with BadRequestException guard
- Narrow details DTO type from unknown to Record<string, unknown>|null
- Add error state UI for API fetch failures
- Add error-path test with static mock import pattern

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

apps/api/src/dashboard/dashboard.controller.ts

@@ -1,8 +1,9 @@
-import { Controller, Get, UseGuards } from "@nestjs/common";
+import { Controller, Get, UseGuards, BadRequestException } from "@nestjs/common";
 import { DashboardService } from "./dashboard.service";
 import { AuthGuard } from "../auth/guards/auth.guard";
 import { WorkspaceGuard, PermissionGuard } from "../common/guards";
 import { Workspace, Permission, RequirePermission } from "../common/decorators";
+import type { DashboardSummaryDto } from "./dto";
 
 /**
  * Controller for dashboard endpoints.
@@ -25,7 +26,10 @@ export class DashboardController {
    */
   @Get("summary")
   @RequirePermission(Permission.WORKSPACE_ANY)
-  async getSummary(@Workspace() workspaceId: string) {
+  async getSummary(@Workspace() workspaceId: string | undefined): Promise<DashboardSummaryDto> {
+    if (!workspaceId) {
+      throw new BadRequestException("Workspace context required");
+    }
     return this.dashboardService.getSummary(workspaceId);
   }
 }

apps/api/src/dashboard/dashboard.service.ts

@@ -142,7 +142,7 @@ export class DashboardService {
       action: row.action,
       entityType: row.entityType,
       entityId: row.entityId,
-      details: row.details,
+      details: row.details as Record<string, unknown> | null,
       userId: row.userId,
       createdAt: row.createdAt.toISOString(),
     }));

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

@@ -17,7 +17,7 @@ export class RecentActivityDto {
   action!: string;
   entityType!: string;
   entityId!: string;
-  details!: unknown;
+  details!: Record<string, unknown> | null;
   userId!: string;
   createdAt!: string;
 }