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.service.ts

@@ -471,6 +471,49 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
     };
   }
 
+  /**
+   * Get driver location history (for route trail display)
+   */
+  async getDriverLocationHistory(
+    driverId: string,
+    fromDate?: Date,
+    toDate?: Date,
+  ): Promise<LocationDataDto[]> {
+    const device = await this.prisma.gpsDevice.findUnique({
+      where: { driverId },
+    });
+
+    if (!device) {
+      throw new NotFoundException('Driver is not enrolled for GPS tracking');
+    }
+
+    // Default to last 4 hours if no date range specified
+    const to = toDate || new Date();
+    const from = fromDate || new Date(to.getTime() - 4 * 60 * 60 * 1000);
+
+    const locations = await this.prisma.gpsLocationHistory.findMany({
+      where: {
+        deviceId: device.id,
+        timestamp: {
+          gte: from,
+          lte: to,
+        },
+      },
+      orderBy: { timestamp: 'asc' },
+    });
+
+    return locations.map((loc) => ({
+      latitude: loc.latitude,
+      longitude: loc.longitude,
+      altitude: loc.altitude,
+      speed: loc.speed,
+      course: loc.course,
+      accuracy: loc.accuracy,
+      battery: loc.battery,
+      timestamp: loc.timestamp,
+    }));
+  }
+
   /**
    * Get driver's own stats (for driver self-view)
    */
@@ -605,28 +648,37 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
       },
     });
 
-    if (devices.length === 0) return;
+    if (devices.length === 0) {
+      this.logger.debug('[GPS Sync] No active devices to sync');
+      return;
+    }
 
     const now = new Date();
+    this.logger.log(`[GPS Sync] Starting sync for ${devices.length} active devices`);
 
     for (const device of devices) {
       try {
-        // Calculate "since" from device's last active time with 5s overlap buffer
+        // Calculate "since" from device's last active time with 30s overlap buffer
+        // (increased from 5s to catch late-arriving positions)
         // Falls back to 2 minutes ago if no lastActive
         const since = device.lastActive
-          ? new Date(device.lastActive.getTime() - 5000)
+          ? new Date(device.lastActive.getTime() - 30000)
           : new Date(now.getTime() - 120000);
 
+        this.logger.debug(`[GPS Sync] Fetching positions for device ${device.traccarDeviceId} since ${since.toISOString()}`);
+
         const positions = await this.traccarClient.getPositionHistory(
           device.traccarDeviceId,
           since,
           now,
         );
 
+        this.logger.log(`[GPS Sync] Device ${device.traccarDeviceId}: Retrieved ${positions.length} positions from Traccar`);
+
         if (positions.length === 0) continue;
 
         // Batch insert with skipDuplicates (unique constraint on deviceId+timestamp)
-        await this.prisma.gpsLocationHistory.createMany({
+        const insertResult = await this.prisma.gpsLocationHistory.createMany({
           data: positions.map((p) => ({
             deviceId: device.id,
             latitude: p.latitude,
@@ -641,6 +693,13 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
           skipDuplicates: true,
         });
 
+        const inserted = insertResult.count;
+        const skipped = positions.length - inserted;
+        this.logger.log(
+          `[GPS Sync] Device ${device.traccarDeviceId}: ` +
+          `Inserted ${inserted} new positions, skipped ${skipped} duplicates`
+        );
+
         // Update lastActive to the latest position timestamp
         const latestPosition = positions.reduce((latest, p) =>
           new Date(p.deviceTime) > new Date(latest.deviceTime) ? p : latest
@@ -650,9 +709,11 @@ Note: GPS tracking is only active during shift hours (${settings.shiftStartHour}
           data: { lastActive: new Date(latestPosition.deviceTime) },
         });
       } catch (error) {
-        this.logger.error(`Failed to sync positions for device ${device.traccarDeviceId}: ${error}`);
+        this.logger.error(`[GPS Sync] Failed to sync positions for device ${device.traccarDeviceId}: ${error}`);
       }
     }
+
+    this.logger.log('[GPS Sync] Sync completed');
   }
 
   /**