Write an index-accelerated proximity query with PostGIS ST_DWithin using geography vs geometry types correctly

Steps

1. Store or cast points as geography to get distance filtering directly in meters via ST_DWithin(geog_col, point, meters)
2. For geometry columns, remember distance is expressed in the SRID's native units (degrees for EPSG:4326) — reproject to a metric SRID first if needed
3. Create a GIST index on the column: CREATE INDEX ... USING GIST (geom_or_geog_col)
4. Use ST_DWithin rather than filtering on ST_Distance for radius queries