feat(content): anti-soup guard on the flow verbs' free-text

Extends structured-content enforcement from the content tools to every
flow verb that carries agent free-text, closing the last hole where a
dev/PM could pass word soup: i_am_blocked(reason), i_am_done(notes),
submit_up/submit_root/complete(notes), escalate_up/escalate_to_ceo(reason),
pass_review(notes), fail_review/pr_fail(issues), pr_pass(notes),
i_documented(notes), delegate(title/description). Plans (i_will_plan /
i_will_work_on) keep their existing >=150-char approach + sub_task gates
and are skipped here so recovery re-entry with thin values still works.

Shared helpers on the choreographer: _free_text_soup (bare envelope, list
aware) and _soup_or_decision_env (folds the soup check into a verb's
existing spec-gate return so no verb gains a return or tips the xenon
bound). reject_trivial now also catches all-filler multi-token strings.

base.md documents the broadened rule for agents.

tests/unit/gateway/test_choreographer_doc.py

@@ -158,7 +158,7 @@ async def test_i_documented_requires_min_notes() -> None:
     deps = _make_deps(task=task_svc, journal=journal_svc)
     c = Choreographer(deps)
 
-    env = await c.i_documented(doc_id, task_id, notes="short", files=["a.md"])
+    env = await c.i_documented(doc_id, task_id, notes="wrote the docs", files=["a.md"])
     body = env.as_dict()
     assert body["error"] == "tracing_gap"
     assert "docs_notes>=min" in body["missing"]