Fix PostGIS geom population: use parseGpxAsync + raw SQL

The initial approach (#150) didn't work because:
1. routes.server.ts used parseGpx (sync, needs browser DOMParser)
   instead of parseGpxAsync (uses linkedom on Node.js) — GPX parsing
   silently failed, so stats AND geom were never populated
2. Drizzle's customType doesn't pass SQL expressions through toDriver

Fixes:
- Switch to parseGpxAsync for all server-side GPX parsing
- Use db.execute() with raw ST_GeomFromGeoJSON SQL after insert
- Remove unused lineStringFromCoords helper from schema
- Share setGeomFromGpx between routes and activities
- Add unit tests for GPX→GeoJSON coordinate extraction

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/gpx/src/geom.test.ts

@@ -0,0 +1,62 @@
+import { describe, it, expect } from "vitest";
+import { parseGpxAsync } from "./parse.ts";
+
+const sampleGpx = `<?xml version="1.0" encoding="UTF-8"?>
+<gpx version="1.1" creator="test" xmlns="http://www.topografix.com/GPX/1/1">
+  <trk>
+    <trkseg>
+      <trkpt lat="52.52" lon="13.405"><ele>34</ele></trkpt>
+      <trkpt lat="51.05" lon="13.74"><ele>113</ele></trkpt>
+      <trkpt lat="48.137" lon="11.576"><ele>519</ele></trkpt>
+    </trkseg>
+  </trk>
+</gpx>`;
+
+describe("GPX to geometry coordinates", () => {
+  it("extracts [lon, lat] coordinates from track points", async () => {
+    const gpxData = await parseGpxAsync(sampleGpx);
+    const coords = gpxData.tracks.flat().map((p) => [p.lon, p.lat] as [number, number]);
+
+    expect(coords).toHaveLength(3);
+    // GeoJSON order: [lon, lat]
+    expect(coords[0]).toEqual([13.405, 52.52]);
+    expect(coords[1]).toEqual([13.74, 51.05]);
+    expect(coords[2]).toEqual([11.576, 48.137]);
+  });
+
+  it("produces valid GeoJSON LineString", async () => {
+    const gpxData = await parseGpxAsync(sampleGpx);
+    const coords = gpxData.tracks.flat().map((p) => [p.lon, p.lat] as [number, number]);
+    const geojson = { type: "LineString", coordinates: coords };
+
+    expect(geojson.type).toBe("LineString");
+    expect(geojson.coordinates).toHaveLength(3);
+    // Verify serialization doesn't throw
+    expect(() => JSON.stringify(geojson)).not.toThrow();
+  });
+
+  it("handles empty GPX gracefully", async () => {
+    const emptyGpx = `<?xml version="1.0" encoding="UTF-8"?>
+    <gpx version="1.1" creator="test" xmlns="http://www.topografix.com/GPX/1/1">
+      <trk><trkseg></trkseg></trk>
+    </gpx>`;
+    const gpxData = await parseGpxAsync(emptyGpx);
+    const coords = gpxData.tracks.flat().map((p) => [p.lon, p.lat] as [number, number]);
+
+    expect(coords).toHaveLength(0);
+  });
+
+  it("handles single point (insufficient for LineString)", async () => {
+    const singlePointGpx = `<?xml version="1.0" encoding="UTF-8"?>
+    <gpx version="1.1" creator="test" xmlns="http://www.topografix.com/GPX/1/1">
+      <trk><trkseg>
+        <trkpt lat="52.52" lon="13.405"><ele>34</ele></trkpt>
+      </trkseg></trk>
+    </gpx>`;
+    const gpxData = await parseGpxAsync(singlePointGpx);
+    const coords = gpxData.tracks.flat().map((p) => [p.lon, p.lat] as [number, number]);
+
+    expect(coords).toHaveLength(1);
+    // Caller should check coords.length >= 2 before creating LineString
+  });
+});