feat(sp10): 277CA parser + Payer-Rejected Inbox lane

- Add cyclone.parsers.models_277ca + parse_277ca (X12 005010X214)
  - Per-Patient HL ClaimStatus with REF*1K (PCN), REF*EJ (tax ID),
    STC category code, amount, service date
  - STC classifier: A1-A3 accepted, A4/A6/A7 rejected, A8/A9 pended,
    P1-P5 paid, anything else unknown
  - Multiple STCs per Patient HL: last wins (canonical pattern for
    'first pended, then paid' acknowledgments)
  - Subscriber-level STCs surface in unscoped_statuses
- Add apply_277ca_rejections — stamps Claim.payer_rejected_* fields on
  matching rows (lookup by patient_control_number, mirrors 999 path)
- New /api/parse-277ca, /api/277ca-acks, /api/277ca-acks/{id} endpoints
- New two77ca_acks table + Two77caAck ORM model
- New Claim columns: payer_rejected_at, _reason, _status_code, _by_277ca_id
- New payer_rejected lane in /api/inbox/lanes (distinct from 999
  envelope rejected lane)
- New PayerConfig277CA block in config/payers.yaml + Pydantic model
- Migration 0008 bumps user_version to 8

Tests: 654 -> 688 (parser 22 + apply 6 + API 8 + config 6 + adjustments).
All 688 backend tests pass; 1 pre-existing skipped test class unaffected.

backend/src/cyclone/store.py

@@ -1800,6 +1800,55 @@ class CycloneStore:
         with db.SessionLocal()() as s:
             return s.get(db.Ta1Ack, ack_id)
 
+    # -- 277CA (SP10) --------------------------------------------------
+
+    def add_277ca_ack(
+        self,
+        *,
+        source_batch_id: str,
+        control_number: str,
+        accepted_count: int,
+        rejected_count: int,
+        paid_count: int,
+        pended_count: int,
+        raw_json: dict,
+    ) -> db.Two77caAck:
+        """Persist a 277CA (Claim Acknowledgment) row and return it.
+
+        Mirrors :meth:`add_ack` but for the claim-level ack. The
+        per-claim status detail stays in ``raw_json``; only the four
+        counts are promoted so the list endpoint stays fast.
+        """
+        with db.SessionLocal()() as s:
+            row = db.Two77caAck(
+                source_batch_id=source_batch_id,
+                control_number=control_number,
+                accepted_count=accepted_count,
+                rejected_count=rejected_count,
+                paid_count=paid_count,
+                pended_count=pended_count,
+                parsed_at=utcnow(),
+                raw_json=raw_json,
+            )
+            s.add(row)
+            s.commit()
+            s.refresh(row)
+            return row
+
+    def list_277ca_acks(self) -> list[db.Two77caAck]:
+        """Return every 277CA ACK row, newest first (auto-increment id desc)."""
+        with db.SessionLocal()() as s:
+            return (
+                s.query(db.Two77caAck)
+                .order_by(db.Two77caAck.id.desc())
+                .all()
+            )
+
+    def get_277ca_ack(self, ack_id: int) -> db.Two77caAck | None:
+        """Return a single 277CA ACK row by id, or ``None`` if not found."""
+        with db.SessionLocal()() as s:
+            return s.get(db.Two77caAck, ack_id)
+
     # -- manual reconciliation (T12) -----------------------------------
 
     def list_unmatched(self, *, kind: str = "both") -> dict: