Board Program LEARN context, ruff 0.16, and verb-rejection observability (#700)

* fix(board): LEARN decisions name the item, not its per-cycle index

A cycle's reject reasons are rendered into the NEXT cycle's exploration
prompt, but the ref recorded alongside each reason was the item's stored
id (item-0/item-1) — a per-cycle index that means something different
every cycle and appears nowhere the explorer can resolve. The reason
survived the loop; what it was about did not.

Record the item's title instead, via a shared learn_ref() helper (falls
back to the id when title-less, and reads target_task_title for Scales,
whose items name the live task they mutate).

* chore(lint): satisfy ruff 0.16 — keyword-only signatures and markdown formatting

The dev toolchain resolved ruff 0.16.0, which stabilises PLR0917 (too many
positional arguments) and formats python code blocks inside markdown. Both
fired repo-wide and neither had anything to do with the code they flagged.

- 36 signatures gain a `*` so their tail arguments are keyword-only, and
  the 104 call sites that passed them positionally are converted. mypy was
  the safety net for the static ones; the full suite caught nine more that
  only bind at runtime (the MCP tool functions, whose real callers already
  pass named JSON arguments).
- 28 markdown files reformatted by 0.16's code-block formatter.
- One RUF036 (`None` mid-union) autofixed in the GitLab provider.

* fix(gateway): log the reason when a verb rejects

A rejected envelope rides an HTTP 200, its body is never logged, and there
is no trace table — so in the access log a verb an agent could not satisfy
looks identical to one that worked. On 2026-07-25 four Board Programs
(Periscope, Sentinel, Scales, Barfly) each POSTed their propose verb three
or four times, persisted nothing, and left their exploration tasks PENDING;
the reason was unrecoverable afterwards, from the logs or from the agents'
own transcripts.

Log error/message/remediate/missing plus the calling agent at
envelope_to_response — the one chokepoint every v1 flow and do route
returns through. Success envelopes stay silent.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/services/test_mirror_service.py

@@ -421,8 +421,11 @@ async def test_approve_records_learn_decision(db_session: AsyncSession) -> None:
         )
     ).scalar_one()
     assert row.items_approved == ONE
+    # The ref is the item's TITLE, not its per-cycle index: this row is
+    # rendered into the next cycle's exploration prompt, where "item-0"
+    # names nothing (see BoardProgramEngine.learn_ref).
     assert {
-        "item_ref": "item-0",
+        "item_ref": "Item 0",
         "verdict": "approved",
         "reason": None,
     } in row.decisions
@@ -445,8 +448,11 @@ async def test_reject_records_learn_decision_with_reason(
         )
     ).scalar_one()
     assert row.items_rejected == ONE
+    # The ref is the item's TITLE, not its per-cycle index: this row is
+    # rendered into the next cycle's exploration prompt, where "item-0"
+    # names nothing (see BoardProgramEngine.learn_ref).
     assert {
-        "item_ref": "item-0",
+        "item_ref": "Item 0",
         "verdict": "rejected",
         "reason": "not a priority",
     } in row.decisions