feat(uploads): add OXICLOUD_CHUNK_DIR + documentation for admins

explain OXICLOUD_CHUNK_DIR and OXICLOUD_UPLOAD_TMPDIR
    and also the OXICLOUD_CHUNK_MAX_BYTES & OXICLOUD_UPLOAD_TMPDIR
    to help administratorrs to defined correctly their storage architecture

docs/config/env.md

@@ -12,6 +12,9 @@ Most runtime variables use the `OXICLOUD_` prefix. A few build-time or allocator
 | `OXICLOUD_SERVER_HOST` | `127.0.0.1` | Server bind address (IPv4 or IPv6 allowed) |
 | `OXICLOUD_BASE_URL` | (auto) | Public base URL for share links; defaults to `http://{host}:{port}` |
 | `OXICLOUD_MAX_UPLOAD_SIZE` | `10737418240` | Maximum upload size in bytes (10 GB on 64-bit, 1 GB on 32-bit) |
+| `OXICLOUD_CHUNK_MAX_BYTES` | `104857600` | Maximum size of a single chunked-upload PUT in bytes (100 MB). Distinct from `OXICLOUD_MAX_UPLOAD_SIZE`, which is the whole-file cap. See [Storage Fine Tuning](./storage-fine-tuning.md). |
+| `OXICLOUD_UPLOAD_TMPDIR` | (OS temp dir) | Spool directory for non-chunked PUT bodies (`/api/files/upload`, WebDAV PUT). Point at a real-disk path on the same FS as `.blobs/` to avoid tmpfs OOMKill and make blob promotion an atomic rename. See [Storage Fine Tuning](./storage-fine-tuning.md). |
+| `OXICLOUD_CHUNK_DIR` | `{STORAGE_PATH}/.uploads` | Root directory for chunked-upload sessions (REST + NextCloud). Same-FS / NVMe placement guidance: see [Storage Fine Tuning](./storage-fine-tuning.md). |
 | `OXICLOUD_REUSE_PORT` | `false` | Enable `SO_REUSEPORT` so multiple processes can share the same port. **Disabled by default** — a second accidental instance will fail with "address already in use". Enable only for deliberate multi-worker setups (process supervisor, rolling restart). Not supported on Windows. |
 
 ## Database