fix: improve GPS position sync reliability and add route trails (#21)

Backend:
- Increase sync overlap buffer from 5s to 30s to catch late-arriving positions
- Add position history endpoint GET /gps/locations/:driverId/history
- Add logging for position sync counts (returned vs inserted)

Frontend:
- Add useDriverLocationHistory hook for fetching position trails
- Draw Polyline route trails on GPS map for each tracked driver
- Historical positions shown as semi-transparent paths behind live markers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/gps/gps.controller.ts

@@ -130,6 +130,21 @@ export class GpsController {
     return location;
   }
 
+  /**
+   * Get a driver's location history (for route trail display)
+   */
+  @Get('locations/:driverId/history')
+  @Roles(Role.ADMINISTRATOR)
+  async getDriverLocationHistory(
+    @Param('driverId') driverId: string,
+    @Query('from') fromStr?: string,
+    @Query('to') toStr?: string,
+  ) {
+    const from = fromStr ? new Date(fromStr) : undefined;
+    const to = toStr ? new Date(toStr) : undefined;
+    return this.gpsService.getDriverLocationHistory(driverId, from, to);
+  }
+
   /**
    * Get a driver's stats (Admin viewing any driver)
    */