Non-multipolygon relations get bounding box as geometry instead of actual geometry

## Description

When processing a planet PBF with `ohsome-planet contributions`, all non-multipolygon relation types receive their bounding box as geometry instead of their actual assembled geometry, even with `--multipolygon-member-limit -1`.

For example, [relation 2195878](https://www.openstreetmap.org/relation/2195878) (Río Aragón,`type=waterway`) outputs a rectangular polygon matching its bbox coordinates exactly:

> POLYGON ((-1.7876927 42.2204245, -1.7876927 42.8105252, -0.5049919 42.8105252, -0.5049919 42.2204245, -1.7876927 42.2204245))

This affects a large number of relations. On a recent planet extract (~1.45 billion features), approximately 5.4 million relations have exactly 5 points (bounding box rectangle). Affected relation types include waterway, route, boundary (non-multipolygon), and others.

## Expected behavior

Relations should have their actual geometry assembled from member ways/nodes, similar to how multipolygon relations are handled via `--multipolygon-member-limit`.

## Steps to reproduce

```bash
ohsome-planet contributions --pbf planet-latest.osm.pbf --data output --multipolygon-member-limit -1
```

Then query the output:

```
-- Show bbox-only relations by type
SELECT tags['type'] as relation_type, COUNT(*) as cnt
FROM 'output/contributions/latest/*.parquet'
WHERE osm_type = 'relation' AND ST_NPoints(geometry) = 5
GROUP BY relation_type ORDER BY cnt DESC;
```

For context, setting `--multipolygon-member-limit` to `-1` (unlimited) only enables geometry assembly for multipolygon relations. It seems there is currently no option to enable geometry assembly for other relation types (waterway, route, boundary, etc.).

Start with the `ohsome-planet contributions` entry point and trace how relation geometry is assembled when `--multipolygon-member-limit -1` is used. Reproduce the issue with the supplied command, then run the DuckDB query against the Parquet output. Done means non-multipolygon relations such as waterway and route relations contain assembled member geometry rather than five-point bounding-box rectangles.

Written by the indexing model from the issue text.