feat(05-01): add Dashboard API route and integration tests

- GET /api/dashboard with read Report permission (ADMIN, OFFICE_STAFF)
- Optional startDate/endDate query params for cash flow date range
- 6 integration tests verifying all metric methods against seeded data
- Tests cover revenue, overdue, subscriber status, cash flow, collectors
- Comprehensive cleanup order for dashboard test data

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

src/app/api/dashboard/route.ts

@@ -0,0 +1,49 @@
+/**
+ * GET /api/dashboard
+ *
+ * Returns all dashboard metrics for the ISP owner's business health overview.
+ * Aggregates revenue, overdue, subscriber status, cash flow, and collector metrics.
+ *
+ * Query params:
+ *   startDate? - ISO date string for cash flow start (default: start of current month)
+ *   endDate?   - ISO date string for cash flow end (default: end of current month)
+ *
+ * Access: ADMIN and OFFICE_STAFF (read Report permission).
+ */
+import { NextRequest, NextResponse } from "next/server";
+import { withPermission } from "@/lib/middleware/authorize";
+import { withTenantContext } from "@/lib/prisma-tenant";
+import { DashboardService } from "@/lib/services/dashboard-service";
+
+export const GET = withPermission("read", "Report")(
+  async (req: NextRequest, { user }) => {
+    if (!user.tenantId) {
+      return NextResponse.json(
+        { error: "No tenant context -- super-admins must use the admin API" },
+        { status: 400 }
+      );
+    }
+
+    const { searchParams } = new URL(req.url);
+    const startDateParam = searchParams.get("startDate");
+    const endDateParam = searchParams.get("endDate");
+
+    const tenantPrisma = withTenantContext(user.tenantId);
+
+    try {
+      const summary = await DashboardService.getDashboardSummary(
+        tenantPrisma,
+        user.tenantId,
+        {
+          startDate: startDateParam ? new Date(startDateParam) : undefined,
+          endDate: endDateParam ? new Date(endDateParam) : undefined,
+        }
+      );
+      return NextResponse.json(summary);
+    } catch (err) {
+      const message =
+        err instanceof Error ? err.message : "Failed to load dashboard";
+      return NextResponse.json({ error: message }, { status: 500 });
+    }
+  }
+);