perf: simplify WFIGS perimeter geometry at query time

Ask ArcGIS for 500 features, 5-decimal precision, and ~250m offset so
fire rings are outlines instead of tens of thousands of vertices.

app/live_layers.py

@@ -597,12 +597,14 @@ async def upsert_vessel(marker: dict) -> None:
         }
 
 
-def _wfigs_params(bbox: str | None) -> dict:
+def _wfigs_params(bbox: str | None, *, offset_m: float = 250.0) -> dict:
     params = {
         "where": "1=1",
         "outSR": "4326",
         "f": "geojson",
-        "resultRecordCount": 2000,
+        "resultRecordCount": 500,
+        "maxAllowableOffset": offset_m / 111_320.0,  # metres → degrees
+        "geometryPrecision": 5,
     }
     if bbox:
         minlon, minlat, maxlon, maxlat = quantize_bbox(*parse_bbox(bbox))

tests/test_live_layers.py

@@ -351,3 +351,14 @@ def test_slim_alert_properties_keeps_popup_fields_only():
         "wfo": "RAH",
         "source": "nws",
     }
+
+
+def test_wfigs_params_requests_simplified_geometry():
+    params = _wfigs_params("-84.5,33.8,-75.4,36.6")
+    assert "maxAllowableOffset" in params
+    assert float(params["maxAllowableOffset"]) > 0
+    assert params["geometryPrecision"] == 5
+    assert int(params["resultRecordCount"]) <= 500
+    # Envelope is the quantized cell, not the raw pan box.
+    geom = params["geometry"]
+    assert geom != "-84.5,33.8,-75.4,36.6"