fix(sp38): restore per-kind control_number in find_ack_orphans + review cleanups

Three pr-reviewer followups from the 2026-07-07 review of commit ad14b56:

1. BUG: find_ack_orphans refactor routed 277ca/ta1 through
   _ack_control_number which only knew 999 — restored per-kind source
   (999 reads raw_json.envelope.control_number, 277ca/ta1 read the ORM
   control_number column). Added regression test pinning all three
   kinds.

2. DOCSTRING DRIFT: reconcile_orphan_st02s said 'remaining columns
   take their defaults' but explicitly passes parsed_at and
   transaction_set_control_number — added both to the explicit list
   and clarified the rest take schema defaults.

3. WASTED SORT: _iter_orphan_999_st02s yielded sorted() but the
   caller re-sorts by (-ack_count, st02) — yielding unsorted now.

Plus three cleanups the reviewer flagged:

* Hoisted 'json' / 'uuid' / 'datetime' imports to module top of
  store/__init__.py (replaced in-method imports).
* Added two missing tests: sentinel grep-discoverability via
  LIKE '<synthetic:%>' + 999-walk tolerance for non-dict raw_json
  (None / list shapes — bytes is unreachable through the ORM).
* Aligned spec/plan exit codes to the cyclone-cli convention
  (exit 1 on DB error, not 2 — matches the existing CLI
  sys.exit(1) and the cyclone-cli skill documentation).

36/36 SP38 tests pass.

docs/superpowers/specs/2026-07-07-cyclone-orphan-ack-housekeeping-design.md

@@ -37,7 +37,9 @@ of remaining forever-orphans.
 - A `cyclone ack-orphans status` CLI subcommand that prints the
   distinct orphan ST02s + ack count per ST02 + the total orphan count
   + the count of orphan rows whose ST02 matches a `batches` row vs
-  those that don't. Deterministic, exit 0 on success / 2 on DB error.
+  those that don't. Deterministic, exit 0 on success / 1 on DB
+  error (matching the `cyclone-cli` skill convention: 1 =
+  unexpected exception, including DB-side errors).
 - A `cyclone ack-orphans reconcile` CLI subcommand that creates
   synthetic `batches` rows for each distinct orphan ST02 that does
   NOT already exist in `batches`. Synthetic rows are marked with
@@ -138,14 +140,17 @@ migration, no UI change, no auto-runnable reconcile.
 Per `cyclone-tests` (autouse conftest at `backend/tests/conftest.py`):
 
 - `backend/tests/test_ack_orphan_summary.py` — new, tests the store
-  helper directly. Parametrised over kind combinations (999 / 277ca
-  / ta1), asserts the summary shape, asserts idempotency of the
-  reconcile insert, asserts the sentinel `input_filename` is
-  preserved, asserts the `kind = '837p'` invariant.
+  helper directly. 999-only (matches the helper's scope; 277ca /
+  ta1 orphans are tracked by `find_ack_orphans(kind)` but their
+  "ST02" semantics differ — see §1 — so they are excluded from
+  the per-ST02 summary). Asserts the summary shape, asserts
+  idempotency of the reconcile insert, asserts the sentinel
+  `input_filename` is preserved, asserts the `kind = '837p'`
+  invariant.
 - `backend/tests/test_ack_orphans_cli.py` — new, tests the CLI
   subcommands via `click.testing.CliRunner` (matching the
-  SP37-followup #5 pattern). Asserts exit codes, stdout shape,
-  idempotency of reconcile.
+  SP37-followup #5 pattern). Asserts exit codes (0 / 1), stdout
+  shape, idempotency of reconcile.
 - No frontend test impact (no UI change).
 - No migration test impact (no schema change; the synthetic batch
   rows are inserted via SQLAlchemy at runtime, not via the