docs: sync docs with current code after refactor

- architecture: remove TaskManager.max_prompt_len (merged into max_seq_len in 53c804e)
- dataflow: fix DatasetFactory.load param name max_position_embeddings -> max_len
- params: add fsdp2 to parallel_mode, add --max_seq_len to server, add 4 missing generate options
- preprocessing: add missing batch_size config field

assets/docs/preprocessing.md

@@ -256,6 +256,7 @@ When `sources` is set, `sections` is ignored.
 | `min_chars` | int | `50` | Skip text-mode items shorter than this |
 | `max_chars` | int | `2000000` | Skip text-mode items longer than this |
 | `max_items` | int or null | `null` | Stop after N documents |
+| `batch_size` | int | `256` | Records per tokenization batch |
 | `packing_strategy` | str | `"simple"` | Packing strategy: `"simple"`, `"bfd"`, `"bfd_split"` |
 | `max_packed_len` | int | `8192` | Maximum length of a packed bin |
 | `truncation_mode` | str | `"keep_start"` | How to truncate sequences: `"keep_start"` or `"keep_end"` |