feat(sp27): server-aggregate Remittances KPIs (count, paid, adjustments)

The Remittances page's three KPI tiles — REMITS / TOTAL PAID /
ADJUSTMENTS — were computed page-locally via items.reduce(...) over
the merged tail of the current page + live delta. With a 100-row
default limit, a 1,739-row population showed count=100, paid=$16,934,
adjustments=$147 — silently understating reality because the page
hadn't loaded the remaining rows yet.

This change mirrors the silent-incompleteness fix that
/api/dashboard/kpis (commit 59c3275) and /api/remittances (commit
d81b6ed) made for their tiles:

  * CycloneStore.summarize_remittances() iterates the full filtered
    remittance population (no limit) and returns
    {count, total_paid, total_adjustments}. Mirrors iter_remittances
    with limit=_ITER_UNBOUNDED.
  * GET /api/remittances/summary — server endpoint with the same
    filter parameters as /api/remittances. Registered BEFORE the
    /api/remittances/stream handler so FastAPI doesn't treat
    'summary' as a stream sub-path.
  * api.listRemittanceSummary + useRemittanceSummary hook.
  * Remittances.tsx swaps off items.reduce, consumes the server
    summary. Tiles render the server totals so the values reflect
    the entire DB population, not the page-local sample.

Verified live: /api/remittances/summary returns
{count: 1739, total_paid: 227181.58, total_adjustments: 13792.65},
which matches DB ground truth exactly.

Tests: 8 new backend tests in test_api_remittances_summary.py; 1 new
frontend test in Remittances.test.tsx (kpi_tiles_use_server_summary_not
_page_local_reduce) plus the page-level test for the zero-valued mock
default.

backend/src/cyclone/api.py

@@ -2241,6 +2241,37 @@ def list_remittances(
     }
 
 
+@app.get("/api/remittances/summary", dependencies=[Depends(matrix_gate)])
+def remittances_summary(
+    batch_id: str | None = Query(None),
+    payer: str | None = Query(None),
+    claim_id: str | None = Query(None),
+    date_from: str | None = Query(None),
+    date_to: str | None = Query(None),
+) -> dict:
+    """Server-aggregated KPI tiles for the Remittances page.
+
+    Returns ``{count, total_paid, total_adjustments}`` over the
+    full filtered remittance population — NOT a page-limited
+    sample. The Remittances page consumes this for its "Total paid"
+    and "Adjustments" tiles so they can't silently understate the
+    true DB population the way a page-local ``items.reduce(...)``
+    would. Mirrors the silent-incompleteness fix that
+    ``/api/dashboard/kpis`` (commit ``59c3275``) and
+    ``/api/remittances`` (commit ``d81b6ed``) made for their tiles.
+
+    Same filter parameters as ``/api/remittances``. Always returns
+    a populated dict (``{"count": 0, "total_paid": 0,
+    "total_adjustments": 0}`` when no rows match) so the frontend
+    can render the tiles directly without a loading-vs-empty
+    branch.
+    """
+    return store.summarize_remittances(
+        batch_id=batch_id, payer=payer, claim_id=claim_id,
+        date_from=date_from, date_to=date_to,
+    )
+
+
 @app.get("/api/remittances/stream", dependencies=[Depends(matrix_gate)])
 async def remittances_stream(
     request: Request,

backend/src/cyclone/store.py

@@ -192,7 +192,7 @@ def _claim_837_row(claim: ClaimOutput, batch_id: str) -> Claim:
         id=claim.claim_id,
         batch_id=batch_id,
         # SP27 Task 17: Claim.patient_control_number must hold the CLM01
-        # claim_submitter's_identifier the 837 sent — that's the value the
+        # claim_submittr's_identifier the 837 sent — that's the value the
         # 835 echoes in CLP01, which the reconcile matcher joins on
         # (reconcile.py:by_pcn), and what 999 / 277CA ACK lookups also
         # use to cross-reference the original claim. Storing
@@ -1826,6 +1826,45 @@ class CycloneStore:
         )
         return len(rows)
 
+    def summarize_remittances(
+        self,
+        *,
+        batch_id: str | None = None,
+        payer: str | None = None,
+        claim_id: str | None = None,
+        date_from: str | None = None,
+        date_to: str | None = None,
+    ) -> dict:
+        """Return ``{count, total_paid, total_adjustments}`` summed
+        over the remittance population that ``iter_remittances``
+        would return under the same filters.
+
+        Same filter parameters as :meth:`iter_remittances` (excluding
+        ``sort``/``order``/``limit``/``offset``). The endpoint that
+        relies on this helper —
+        ``GET /api/remittances/summary`` — backs the Remittances
+        page's KPI tiles so a page-local sum (25 rows + live-tail
+        delta) can never silently understate the true population.
+        Mirrors Dashboard's server-aggregated ``/api/dashboard/kpis``
+        (commit ``59c3275``) and the ``count_remittances`` shape
+        from commit ``d81b6ed``.
+        """
+        rows = self.iter_remittances(
+            batch_id=batch_id, payer=payer, claim_id=claim_id,
+            date_from=date_from, date_to=date_to,
+            sort=None, order="desc", limit=_ITER_UNBOUNDED, offset=0,
+        )
+        total_paid = 0.0
+        total_adjustments = 0.0
+        for r in rows:
+            total_paid += float(r.get("paidAmount") or 0)
+            total_adjustments += float(r.get("adjustmentAmount") or 0)
+        return {
+            "count": len(rows),
+            "total_paid": total_paid,
+            "total_adjustments": total_adjustments,
+        }
+
     def distinct_providers(self) -> list[dict]:
         """Group claims by NPI and return one row per provider."""
         with db.SessionLocal()() as s: