Add document storage (local filesystem) + fix dashboard outstanding KPI

- Local file storage via STORAGE_PATH env var (replaces DO Spaces)
- POST/GET/DELETE /api/cases/:caseId/documents + GET /api/documents/:docId/download
- useDocuments hook + upload/list/download/delete UI in CaseDetailPage
- GET /api/invoices/summary — live SUM of sent+overdue invoices
- Dashboard outstanding KPI wired to real DB value
- api.upload() for FormData, formatBytes() utility

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

apps/web/src/hooks/useDocuments.ts

@@ -0,0 +1,40 @@
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
+import { api, type ApiError } from '@/lib/api';
+
+export interface Document {
+  id: string;
+  name: string;
+  mimeType: string;
+  sizeBytes: number;
+  createdAt: string;
+}
+
+const KEY = (caseId: string) => ['documents', caseId] as const;
+
+export function useDocuments(caseId: string | undefined) {
+  return useQuery<Document[]>({
+    queryKey: caseId ? KEY(caseId) : ['documents', 'noop'],
+    queryFn: () => api.get(`/api/cases/${caseId}/documents`),
+    enabled: !!caseId,
+  });
+}
+
+export function useUploadDocument(caseId: string) {
+  const qc = useQueryClient();
+  return useMutation<Document, ApiError, File>({
+    mutationFn: (file) => {
+      const form = new FormData();
+      form.append('file', file);
+      return api.upload(`/api/cases/${caseId}/documents`, form);
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: KEY(caseId) }),
+  });
+}
+
+export function useDeleteDocument(caseId: string) {
+  const qc = useQueryClient();
+  return useMutation<void, ApiError, string>({
+    mutationFn: (docId) => api.delete(`/api/documents/${docId}`),
+    onSuccess: () => qc.invalidateQueries({ queryKey: KEY(caseId) }),
+  });
+}

apps/web/src/hooks/useInvoices.ts

@@ -90,6 +90,13 @@ function qs(p: ListParams): string {
   return s ? `?${s}` : '';
 }
 
+export function useInvoiceSummary() {
+  return useQuery<{ outstanding: string }>({
+    queryKey: ['invoices', 'summary'],
+    queryFn: () => api.get('/api/invoices/summary'),
+  });
+}
+
 export function useInvoices(params: ListParams = {}) {
   return useQuery<ListResponse>({
     queryKey: KEY.list(params),