feat(render): add --line-scale option for road line thickness - #194

Problem

When generating posters for small areas (e.g. individual districts or neighborhoods), the default road line thickness produces very thin, hard-to-see roads because the zoom level makes the area roads too fine.

Solution

Add a --line-scale option that applies a multiplier to road line thickness. This allows users to increase thickness when rendering small areas where the defaults are insufficient.

Usage:

uv run ./create_map_poster.py --city "Stadtwald" --country "Marburg" -lat 50.7906111111 -long 8.73826111111 -d 1650 --line-scale 5

Before / After

Stadtwald: a small neighbourhood

--line-scale 1 (Default) vs --line-scale 5

Before	After

With default line thickness, roads in small-area maps like Stadtwald or neighbourhoods are very thin and hard to see. With an increased --line-scale value, roads become clearly visible.