docs: list claims.py in api_routers/ Project layout

Another router extraction landed: api_routers/claims.py now owns the
five /api/claims[...] routes (list, stream, detail, serialize-837,
line-reconciliation). Pure code-organization move from api.py — no
new endpoints, no new functionality.

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

README.md

@@ -482,6 +482,8 @@ backup API).
 │   │   │   ├── ta1_acks.py    #   GET /api/ta1-acks, /api/ta1-acks/{id}
 │   │   │   ├── activity.py    #   GET /api/activity, /api/activity/stream
 │   │   │   ├── 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
 │   │   │   ├── 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