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/tests/test_acks.py

@@ -51,17 +51,17 @@ def test_migration_0002_creates_acks_table():
 
 def test_migration_latest_idempotent_on_fresh_db():
     """Re-running the migration on the same DB must be a no-op (PRAGMA
-    user_version already at the latest version — currently 7 after
-    0004-0006 line_reconciliation, 0005 ta1_acks, and SP9's 0007
-    providers/payers/clearhouse)."""
+    user_version already at the latest version — currently 8 after
+    0004-0006 line_reconciliation, 0005 ta1_acks, SP9's 0007
+    providers/payers/clearhouse, and SP10's 0008 payer_rejected)."""
     with db.engine().begin() as c:
         v1 = c.exec_driver_sql("PRAGMA user_version").scalar() or 0
-    assert v1 == 7
+    assert v1 == 8
     # A second run should not raise and should not bump the version.
     db_migrate.run(db.engine())
     with db.engine().begin() as c:
         v2 = c.exec_driver_sql("PRAGMA user_version").scalar() or 0
-    assert v2 == 7
+    assert v2 == 8
 
 
 def test_add_ack_persists_row():