annotate: dedup task_aug + row-normalization; docs module on/off table

Two behavior-preserving simplifications:
  * plan_subtasks_memory.run_episode: the task_aug 'axes' and free-form
    branches built identical deduped rows via copy-pasted seen/append
    loops. Collapse to one branch that picks the variant source, then a
    shared _task_aug_rows() helper does the dedup + row build (-~25 LOC).
  * writer: _normalize_persistent_row / _normalize_event_row shared the
    same camera-validate + struct construction. Extract _normalize_row(),
    keeping the exact key order (the parquet struct schema is inferred
    from insertion order, so timestamp must stay between style and camera).

docs: 'Which modules run' is now a table giving each module's on/off flag
(--plan.enabled / --interjections.enabled / --vqa.enabled) and what it
turns off.

Verified: 40 tests pass (incl. test_writer struct round-trip); pre-commit clean.

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

docs/source/annotation_pipeline.mdx

@@ -136,9 +136,14 @@ short manipulation episodes.
 
 ### Which modules run
 
-Each module can be turned off independently to iterate on one at a time:
-`--plan.enabled`, `--interjections.enabled`, `--vqa.enabled` (all
-`true` by default).
+Every module is on by default and can be toggled independently (set to
+`false` to skip it, e.g. to iterate on one module at a time):
+
+| Flag                      | Default | Turns off                           |
+| ------------------------- | ------- | ----------------------------------- |
+| `--plan.enabled`          | `true`  | subtasks + plan + memory + task_aug |
+| `--interjections.enabled` | `true`  | interjections + speech atoms        |
+| `--vqa.enabled`           | `true`  | the VQA pairs                       |
 
 ### The VLM (`--vlm.*`)