feat: language annotation pipeline (PR 2/3)

Adds the steerable annotation pipeline (`lerobot-annotate`) that populates
the `language_persistent` and `language_events` columns introduced in
PR 1 directly into `data/chunk-*/file-*.parquet`. No flavor namespace,
no sidecar tree.

Modules produced:
- Module 1 (plan_subtasks_memory): Pi0.7-style subtasks, plan (init +
  refresh on interjection), MEM-style memory at subtask boundaries.
- Module 2 (interjections_and_speech): t=0 speech-only acknowledgement,
  mid-episode paired interjection + speech tool-call atom.
- Module 3 (general_vqa): bbox/keypoint/count/attribute/spatial pairs at
  configurable cadence with one-retry JSON validation.

Writer enforces: per-episode persistent identity, exact-frame event
timestamps, column routing per `column_for_style`, dataset-level `tools`
column with the `say` schema, drops legacy `subtask_index`. Validator
runs against staged JSONL artifacts before the writer rewrites parquet.

Adds `lerobot-annotate` console script, `annotations` extra (datatrove +
optional vllm), `make annotation-e2e` opt-in smoke target, and
`docs/source/annotation_pipeline.mdx`.

Branched from PR 1 (`feat/language-columns`).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lerobot/annotations/steerable_pipeline/__init__.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Steerable annotation pipeline producing ``language_persistent`` and
+``language_events`` columns for LeRobot datasets.
+
+The pipeline is decomposed into three independently runnable modules whose
+outputs are staged per-episode before a final parquet rewrite:
+
+- :mod:`.modules.plan_subtasks_memory` (Module 1) — persistent styles
+- :mod:`.modules.interjections_and_speech` (Module 2) — event styles + speech
+- :mod:`.modules.general_vqa` (Module 3) — event-style VQA pairs
+"""
+
+from .config import AnnotationPipelineConfig
+from .validator import StagingValidator, ValidationReport
+from .writer import LanguageColumnsWriter
+
+__all__ = [
+    "AnnotationPipelineConfig",
+    "LanguageColumnsWriter",
+    "StagingValidator",
+    "ValidationReport",
+]