fix(stats): use accumulated elevation gain for Most Climbing record

The Most Climbing record was incorrectly using net climb (endElevation - startElevation)
instead of accumulated elevation gain. This caused two problems:
1. Net climb doesn't capture drives that go up and down (e.g., +500m up, -400m down = +100m net vs +500m accumulated)
2. Many drives have null endElevation, causing them to be excluded from the query

Fixed by:
- Updated AggregateDao queries to ORDER BY elevationGain (accumulated) instead of (endElevation - startElevation)
- Updated queries to filter by elevationGain IS NOT NULL instead of requiring both start/end elevations
- Simplified StatsRepository to use elevationGain directly instead of recalculating net climb

app/src/main/java/com/matedroid/data/local/dao/AggregateDao.kt

@@ -81,13 +81,12 @@ interface AggregateDao {
     """)
     suspend fun driveWithMinElevation(carId: Int): DriveDetailAggregate?
 
-    // Drive with most net elevation gain (end - start altitude)
+    // Drive with most accumulated elevation gain (total meters climbed)
     @Query("""
         SELECT a.* FROM drive_detail_aggregates a
         WHERE a.carId = :carId
-        AND a.startElevation IS NOT NULL
-        AND a.endElevation IS NOT NULL
-        ORDER BY (a.endElevation - a.startElevation) DESC LIMIT 1
+        AND a.elevationGain IS NOT NULL
+        ORDER BY a.elevationGain DESC LIMIT 1
     """)
     suspend fun driveWithMostElevationGain(carId: Int): DriveDetailAggregate?
 
@@ -95,10 +94,9 @@ interface AggregateDao {
         SELECT a.* FROM drive_detail_aggregates a
         JOIN drives_summary d ON a.driveId = d.driveId
         WHERE a.carId = :carId
-        AND a.startElevation IS NOT NULL
-        AND a.endElevation IS NOT NULL
+        AND a.elevationGain IS NOT NULL
         AND d.startDate >= :startDate AND d.startDate < :endDate
-        ORDER BY (a.endElevation - a.startElevation) DESC LIMIT 1
+        ORDER BY a.elevationGain DESC LIMIT 1
     """)
     suspend fun driveWithMostElevationGainInRange(carId: Int, startDate: String, endDate: String): DriveDetailAggregate?
 

app/src/main/java/com/matedroid/data/repository/StatsRepository.kt

@@ -176,14 +176,10 @@ class StatsRepository @Inject constructor(
             },
             driveWithMostClimbing = driveWithMostGain?.let { agg ->
                 val drive = driveSummaryDao.get(agg.driveId)
-                // Net elevation gain = end elevation - start elevation
-                val netElevationGain = if (agg.startElevation != null && agg.endElevation != null) {
-                    agg.endElevation - agg.startElevation
-                } else null
                 DriveElevationRecord(
                     driveId = agg.driveId,
                     elevationM = agg.maxElevation ?: 0,
-                    elevationGainM = netElevationGain,
+                    elevationGainM = agg.elevationGain,
                     date = drive?.startDate
                 )
             },
@@ -283,13 +279,10 @@ class StatsRepository @Inject constructor(
             driveWithMinElevation = null, // Not shown in UI
             driveWithMostClimbing = driveWithMostGain?.let { agg ->
                 val drive = driveSummaryDao.get(agg.driveId)
-                val netElevationGain = if (agg.startElevation != null && agg.endElevation != null) {
-                    agg.endElevation - agg.startElevation
-                } else null
                 DriveElevationRecord(
                     driveId = agg.driveId,
                     elevationM = agg.maxElevation ?: 0,
-                    elevationGainM = netElevationGain,
+                    elevationGainM = agg.elevationGain,
                     date = drive?.startDate
                 )
             },