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/db/src/schema/journal.ts

@@ -7,7 +7,6 @@ import {
   jsonb,
   customType,
 } from "drizzle-orm/pg-core";
-import { sql, type SQL } from "drizzle-orm";
 
 const bytea = customType<{ data: Buffer }>({
   dataType() {
@@ -15,27 +14,12 @@ const bytea = customType<{ data: Buffer }>({
   },
 });
 
-const lineString = customType<{ data: string | SQL }>({
+const lineString = customType<{ data: string }>({
   dataType() {
     return "geometry(LineString, 4326)";
   },
-  toDriver(value) {
-    return value;
-  },
 });
 
-/**
- * Build a SQL expression to create a PostGIS LineString from coordinate pairs.
- * Coordinates are [lon, lat] (GeoJSON order).
- */
-export function lineStringFromCoords(coords: [number, number][]): SQL {
-  const geojson = JSON.stringify({
-    type: "LineString",
-    coordinates: coords,
-  });
-  return sql`ST_GeomFromGeoJSON(${geojson})`;
-}
-
 export const journalSchema = pgSchema("journal");
 
 export const users = journalSchema.table("users", {