docs: list remittances.py in api_routers/ Project layout

Another router extraction landed: api_routers/remittances.py now owns
the three /api/remittances[...] routes (list, stream, detail). Pure
code-organization move from api.py — no new endpoints, no new
functionality.

Update the Project layout block to list remittances.py alongside the
other 9 routers with the routes it owns.

README.md

@@ -484,6 +484,7 @@ backup API).
 │   │   │   ├── batches.py     #   GET /api/batches, /api/batches/{id}, /api/batch-diff
 │   │   │   ├── claims.py      #   GET /api/claims, /api/claims/stream, /api/claims/{id},
 │   │   │   │                  #   /api/claims/{id}/serialize-837, /api/claims/{id}/line-reconciliation
+│   │   │   ├── remittances.py #   GET /api/remittances, /api/remittances/stream, /api/remittances/{id}
 │   │   │   ├── providers.py   #   GET /api/providers
 │   │   │   ├── clearhouse.py  #   GET /api/clearhouse, POST /api/clearhouse/submit
 │   │   │   └── config.py      #   /api/config/providers[/...], /api/config/payers[/...], /api/admin/reload-config