feat(sp7): wire _reconcile_pair into manual_match (T21)

manual_match previously only flipped the claim↔remit FK and the
claim state — it never ran line-level reconciliation, so manually-
paired claims surfaced empty line-reconciliation rows to the UI
and skipped CLP-level CAS aggregate recompute.

Refactor reconcile.run() to call a new per-pair helper
_reconcile_pair(session, claim, remittance) that:
  - clears any existing LineReconciliation rows for the claim
    (idempotent re-run; safe across manual_unmatch + manual_rematch
    cycles that may pair the claim with a different remittance),
  - reads 837 SV1 lines from Claim.raw_json and 835 SVC rows from
    ServiceLinePayment,
  - runs match_service_lines() and persists a LineReconciliation row
    per side,
  - recomputes Remittance.claim_level_adjustment_amount (CLP-level
    CAS) and Remittance.adjustment_amount (total CAS).

manual_match now calls this helper after the FK is set and before
commit, mirroring the auto-match path. Reversals are skipped (they
don't have SV1↔SVC line pairs; per §7.3).

Tests (test_store_reconcile.py):
  - test_manual_match_populates_line_reconciliation_rows: end-to-end
    check that a manual pair writes the expected matched +
    unmatched_837_only rows plus zero CAS aggregates.
  - test_manual_match_idempotent_line_reconciliation: after
    manual_unmatch + manual_rematch + inserting a CLP-level CAS row
    directly, the claim has exactly two fresh LineReconciliation rows
    (no duplicates) and the remittance aggregate reflects the new CAS.

Smoke tested end-to-end via TestClient: parse co_medicaid_837p.txt
+ co_medicaid_835.txt, auto-matcher skips (PCNs differ), manual
match via POST /api/reconciliation/match, then
GET /api/claims/{id}/line-reconciliation returns 2 rows and
GET /api/inbox/lanes shows matched_remittance.total_lines=2.

Note: matched_lines may be 0 on real 835 fixtures due to a
pre-existing parser bug in _consume_service_payment that swaps
SVC04 (units) and SVC05 (unit-of-measure) when reading units from
the segment. The SP7 strict-match criterion requires units parity,
so the misread produces None on the SVC side and strict-match
never succeeds. Surfaced as a follow-up; the SP7 work itself is
correct (line counts are computed and persisted).

backend/src/cyclone/store.py

@@ -1948,6 +1948,11 @@ class CycloneStore:
             # we don't rely on T10 to do this.
             remit.claim_id = claim_id
 
+            # SP7: line-level reconciliation + claim-level CAS aggregate.
+            # Skipped for reversals — they don't have SV1↔SVC line pairs.
+            if not remit.is_reversal:
+                _reconcile._reconcile_pair(s, claim, remit)
+
             s.add(ActivityEvent(
                 ts=now,
                 kind="manual_match",