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/api/src/routes/invoices.ts

@@ -115,6 +115,16 @@ export async function invoicesRoutes(app: FastifyInstance) {
     return { items: rows, total: count?.total ?? 0 };
   });
 
+  // Summary — outstanding total across sent + overdue invoices
+  app.get('/api/invoices/summary', async (req) => {
+    const firmId = req.user!.firmId!;
+    const [row] = await getDb()
+      .select({ outstanding: sql<string>`COALESCE(SUM(${invoices.total}), 0)` })
+      .from(invoices)
+      .where(and(eq(invoices.firmId, firmId), inArray(invoices.status, ['sent', 'overdue'])));
+    return { outstanding: row?.outstanding ?? '0' };
+  });
+
   // Get with items
   app.get('/api/invoices/:id', async (req, reply) => {
     const firmId = req.user!.firmId!;