Add configurable polygon-based geographic filter for nodes

We should add a configurable geographic filter based on a polygon so nodes outside a defined region are hidden. Problem Right now, any node with a valid position shows up, even if it’s clearly outside the intended coverage area. This leads to: • map clutter • misleading stats • noise from distant nodes or bad GPS fixes A bounding box isn’t sufficient for many real-world regions. Proposal • Add a polygon-based bounds filter • Nodes outside the polygon are excluded from UI/API results • Data is still ingested and stored (no deletion) Config • polygon required (GeoJSON or WKT) Implementation notes • Filter at query/API layer • Postgres + PostGIS would support this cleanly (ST_Contains / ST_Within) • Could expose a “displayable nodes” view if needed Goal Make deployments region-aware and reduce noise without losing underlying data.