Health Connect: Add DistanceSyncer for daily activity distance

Syncs device-reported distance (distanceCm) from ActivitySamples to
Health Connect DistanceRecord. Only writes actual device measurements,
skips NOT_MEASURED or zero values.

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/healthconnect/syncers/DistanceSyncer.kt

@@ -0,0 +1,57 @@
+/*  Copyright (C) 2025 Gideon Zenz
+
+    This file is part of Gadgetbridge.
+
+    Gadgetbridge is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Gadgetbridge is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>. */
+package nodomain.freeyourgadget.gadgetbridge.util.healthconnect.syncers
+
+import androidx.health.connect.client.records.DistanceRecord
+import androidx.health.connect.client.records.metadata.Metadata
+import androidx.health.connect.client.units.Length
+import nodomain.freeyourgadget.gadgetbridge.model.ActivitySample
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+import java.time.Instant
+import java.time.ZoneOffset
+import java.time.temporal.ChronoUnit
+import kotlin.reflect.KClass
+
+internal object DistanceSyncer : AbstractActivitySampleSyncer<DistanceRecord>() {
+    override val logger: Logger = LoggerFactory.getLogger(DistanceSyncer::class.java)
+    override val recordClass: KClass<DistanceRecord> = DistanceRecord::class
+
+    override fun convertSample(
+        sample: ActivitySample,
+        offset: ZoneOffset,
+        metadata: Metadata,
+        deviceName: String
+    ): DistanceRecord? {
+        val distanceCm = sample.distanceCm
+        if (distanceCm <= 0 || distanceCm == ActivitySample.NOT_MEASURED) {
+            return null
+        }
+
+        val endTs = Instant.ofEpochSecond(sample.timestamp.toLong())
+        val startTs = endTs.minus(1, ChronoUnit.MINUTES)
+
+        return DistanceRecord(
+            startTime = startTs,
+            startZoneOffset = offset,
+            endTime = endTs,
+            endZoneOffset = offset,
+            distance = Length.meters(distanceCm / 100.0),
+            metadata = metadata
+        )
+    }
+}