fix: nil slice -> empty slice in list API responses

Backend:
- ListStorageJobs, ListSambaShares, ListNFSExports, ListUsers,
  ListDirty, ListApplyLog, ListWatchedMounts: initialize with
  make([]T, 0) instead of var x []T to avoid JSON null on empty.
  Fixes "Cannot read properties of null" crash on /storage.

Frontend:
- Storage.tsx: defensive setJobs(res.jobs ?? []) to guard against
  API returning null.

Tests:
- Add TestListStorageJobsEmptyReturnsSlice.

Version: 0.7.1

web/tsconfig.tsbuildinfo

@@ -0,0 +1 @@
+{"root":["./src/app.tsx","./src/dirtycontext.tsx","./src/api.ts","./src/main.tsx","./src/components/dirtybanner.tsx","./src/components/filebrowsermodal.tsx","./src/components/layout.tsx","./src/components/modal.tsx","./src/components/pathfield.tsx","./src/pages/dashboard.tsx","./src/pages/files.tsx","./src/pages/log.tsx","./src/pages/login.tsx","./src/pages/nfs.tsx","./src/pages/samba.tsx","./src/pages/settings.tsx","./src/pages/storage.tsx","./src/pages/users.tsx"],"version":"5.9.3"}