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>

docs/rag/roles/product-owner.md

@@ -107,8 +107,12 @@ Biweekly cron, project-scoped (`projects.board_programs` contains `"spackle"`).
 propose_gap_fill(
     items=[
         {
-            "title": "...", "description": "...", "acceptance_criteria": ["..."],
-            "project_slug": "roboco-api", "team": "backend", "priority": 2,
+            "title": "...",
+            "description": "...",
+            "acceptance_criteria": ["..."],
+            "project_slug": "roboco-api",
+            "team": "backend",
+            "priority": 2,
             "evidence": "BOTH sides of the gap — REQUIRED",
         },
         # 1-5 items
@@ -146,8 +150,12 @@ Event-triggered only (a release-publish hook, or the CEO's "run now") — no cro
 propose_friction_fixes(
     items=[
         {
-            "title": "...", "description": "...", "acceptance_criteria": ["..."],
-            "project_slug": "roboco-api", "team": "frontend", "priority": 2,
+            "title": "...",
+            "description": "...",
+            "acceptance_criteria": ["..."],
+            "project_slug": "roboco-api",
+            "team": "frontend",
+            "priority": 2,
             "evidence": "the walked path (which pages, which clicks) — prose only, never a screenshot — REQUIRED",
         },
         # 1-5 items