feat: cancel button on active downloads

- ActiveDownload now carries workerId (UUID string) for cancellation
- cancelDownload() calls WorkManager.cancelWorkById()
- Downloads tab shows ✕ button on in-progress download cards

android/app/src/main/java/com/yarisobd/app/DashcamViewModel.kt

@@ -23,6 +23,7 @@ import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
 import kotlinx.serialization.json.Json
 import java.io.File
+import java.util.UUID
 
 data class DownloadProgress(
     val path: String,
@@ -37,8 +38,9 @@ data class DownloadedFile(
 )
 
 data class ActiveDownload(
+    val workerId: String,  // UUID string to cancel
     val filename: String,
-    val progress: Int,   // 0-100
+    val progress: Int,
     val done: Boolean,
 )
 
@@ -140,19 +142,19 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
             .build()
 
         val wm = WorkManager.getInstance(getApplication())
+        val uuid = request.id
+        val workerId = uuid.toString()
         wm.enqueue(request)
 
-        // Observe progress
-        val workerId = request.id
-        _activeDownloads.value = _activeDownloads.value + (filename to ActiveDownload(filename, 0, false))
+        _activeDownloads.value = _activeDownloads.value + (filename to ActiveDownload(workerId, filename, 0, false))
 
-        wm.getWorkInfoByIdLiveData(workerId).observeForever { info ->
+        wm.getWorkInfoByIdLiveData(uuid).observeForever { info ->
             if (info == null) return@observeForever
 
             val progress = info.progress.getInt("pct", 0)
             val done = info.state == WorkInfo.State.SUCCEEDED || info.state == WorkInfo.State.FAILED
 
-            _activeDownloads.value = _activeDownloads.value + (filename to ActiveDownload(filename, progress, done))
+            _activeDownloads.value = _activeDownloads.value + (filename to ActiveDownload(workerId, filename, progress, done))
 
             when (info.state) {
                 WorkInfo.State.SUCCEEDED -> {
@@ -169,7 +171,7 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
                     }
                     _activeDownloads.value = _activeDownloads.value - filename
                 }
-                else -> {} // running / enqueued
+                else -> {}
             }
         }
 
@@ -197,6 +199,17 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
         }
     }
 
+    fun cancelDownload(dl: ActiveDownload) {
+        try {
+            val uuid = java.util.UUID.fromString(dl.workerId)
+            WorkManager.getInstance(getApplication()).cancelWorkById(uuid)
+            _activeDownloads.value = _activeDownloads.value - dl.filename
+            viewModelScope.launch {
+                _downloadEvents.emit("✕ Cancelled: ${dl.filename}")
+            }
+        } catch (_: Exception) {}
+    }
+
     fun deleteVideo(video: VideoFile) {
         viewModelScope.launch {
             try {

android/app/src/main/java/com/yarisobd/app/DownloadsScreen.kt

@@ -37,6 +37,7 @@ fun DownloadsScreen(
     files: List<DownloadedFile>,
     activeDownloads: Map<String, ActiveDownload>,
     onDelete: (DownloadedFile) -> Unit,
+    onCancel: (ActiveDownload) -> Unit,
     onRefresh: () -> Unit,
 ) {
     val context = LocalContext.current
@@ -80,11 +81,29 @@ fun DownloadsScreen(
                         )
                     ) {
                         Column(modifier = Modifier.padding(12.dp)) {
+                            Row(
+                                modifier = Modifier.fillMaxWidth(),
+                                horizontalArrangement = Arrangement.SpaceBetween,
+                                verticalAlignment = Alignment.CenterVertically
+                            ) {
                                 Text(
                                     text = if (dl.done) "✓ $filename" else "⏳ $filename",
                                     style = MaterialTheme.typography.bodyMedium,
-                                color = MaterialTheme.colorScheme.onSurface
+                                    color = MaterialTheme.colorScheme.onSurface,
+                                    modifier = Modifier.weight(1f)
                                 )
+                                if (!dl.done) {
+                                    Button(
+                                        onClick = { onCancel(dl) },
+                                        colors = ButtonDefaults.buttonColors(
+                                            containerColor = MaterialTheme.colorScheme.error
+                                        ),
+                                        modifier = Modifier.height(32.dp)
+                                    ) {
+                                        Text("✕", style = MaterialTheme.typography.bodySmall)
+                                    }
+                                }
+                            }
                             if (!dl.done) {
                                 Spacer(modifier = Modifier.height(4.dp))
                                 LinearProgressIndicator(

android/app/src/main/java/com/yarisobd/app/MainActivity.kt

@@ -105,9 +105,10 @@ fun YarisMainScreen(client: OkHttpClient) {
                     onDelete = { dashcamVm.deleteVideo(it) },
                 )
                 1 -> DownloadsScreen(
-                    activeDownloads = activeDownloads,
                     files = downloadedFiles,
+                    activeDownloads = activeDownloads,
                     onDelete = { dashcamVm.deleteDownloaded(it) },
+                    onCancel = { dashcamVm.cancelDownload(it) },
                     onRefresh = { dashcamVm.scanDownloads() },
                 )
                 2 -> DualNetworkTestScreen(