fix(sp28): align Batch.kind filter with prod ('837p' not '837')

The SP28 helpers (batch_envelope_index + lookup_claims_for_ack_set_response
+ two _batch_lookup closures in handle_ta1 + api.py) all filter
Batch.kind == "837", but prod Batch rows are persisted with
kind="837p" (lowercase p — see api.py:443 / store/records.py:58).
Result: the D10 batch-envelope index was empty on prod and zero 999 /
277CA / TA1 acks auto-linked to their claims via Pass 1 (ST02 via
batch.envelope.control_number). Pass 2 (PCN) was the only path firing,
which on this codebase matches 0 acks (Gainwell's 999 echoes the 837's
ST02, not its CLM01 — see spec §D10).

Fix: 4 production sites swapped to Batch.kind == "837p". 3 test
files updated to use the prod value (test_apply_claim_ack_links.py +
test_api_claim_acks.py + test_e2e_999_to_claim_drawer.py). All 25 SP28
tests + 20 handler tests pass. Expected prod effect: claim
t991102989o1c120d's 143 incoming 999 AK2 acks now auto-link via the
batch with envelope.control_number=991102989 (Pass 1), plus 727/1,398
total acks across all batches.

backend/src/cyclone/api.py

@@ -941,7 +941,7 @@ async def parse_ta1_endpoint(
             rows = (
                 link_s.query(Batch)
                 .filter(
-                    Batch.kind == "837",
+                    Batch.kind == "837p",
                     Batch.raw_result_json.isnot(None),
                 )
                 .order_by(Batch.parsed_at.desc())

backend/src/cyclone/claim_acks.py

@@ -141,7 +141,7 @@ def lookup_claims_for_ack_set_response(
         # callers SHOULD pass the index.
         rows = (
             session.query(Batch.id, Batch.raw_result_json)
-            .filter(Batch.kind == "837")
+            .filter(Batch.kind == "837p")
             .all()
         )
         for bid, raw in rows:

backend/src/cyclone/handlers/handle_ta1.py

@@ -75,7 +75,7 @@ def handle(
             rows = (
                 session.query(db.Batch)
                 .filter(
-                    db.Batch.kind == "837",
+                    db.Batch.kind == "837p",
                     db.Batch.raw_result_json.isnot(None),
                 )
                 .order_by(db.Batch.parsed_at.desc())

backend/src/cyclone/store/claim_acks.py

@@ -78,7 +78,7 @@ def batch_envelope_index() -> dict[str, str]:
     with db.SessionLocal()() as s:
         rows = (
             s.query(Batch.id, Batch.raw_result_json)
-            .filter(Batch.kind == "837")
+            .filter(Batch.kind == "837p")
             .all()
         )
         for bid, raw in rows: