feat: server-presence indicator on Downloads tab

- CredentialStore tracks uploaded filenames in prefs
- UploadWorker success marks file as uploaded
- Downloads tab shows green CloudDone icon next to files already on server
- Upload button skipped for files already on server (dedup)

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

@@ -94,6 +94,10 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
     private val _uploadProgress = MutableStateFlow<Map<String, ActiveDownload>>(emptyMap())
     val uploadProgress: StateFlow<Map<String, ActiveDownload>> = _uploadProgress.asStateFlow()
 
+    // Files already on server (filename set)
+    private val _uploadedNames = MutableStateFlow<Set<String>>(emptySet())
+    val uploadedNames: StateFlow<Set<String>> = _uploadedNames.asStateFlow()
+
     // USB dashcam state
     private val _dashcamFiles = MutableStateFlow<List<DashcamFile>>(emptyList())
     val dashcamFiles: StateFlow<List<DashcamFile>> = _dashcamFiles.asStateFlow()
@@ -117,6 +121,7 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
     init {
         loadVideos()
         scanDownloads()
+        _uploadedNames.value = CredentialStore.getUploaded(getApplication())
     }
 
     fun loadVideos() {
@@ -318,6 +323,8 @@ class DashcamViewModel(application: Application) : AndroidViewModel(application)
 
             when (info.state) {
                 WorkInfo.State.SUCCEEDED -> {
+                    CredentialStore.markUploaded(getApplication(), file.name)
+                    _uploadedNames.value = CredentialStore.getUploaded(getApplication())
                     viewModelScope.launch { _downloadEvents.emit("✓ Uploaded: ${file.name}") }
                     _uploadProgress.value = _uploadProgress.value - file.name
                 }

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

@@ -32,6 +32,7 @@ import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.CloudUpload
+import androidx.compose.material.icons.filled.CloudDone
 import androidx.compose.material.icons.filled.Delete
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
@@ -61,6 +62,7 @@ fun DownloadsScreen(
     activeUploads: Map<String, ActiveDownload>,
     deletingNames: Set<String>,
     credentialsConfigured: Boolean,
+    uploadedNames: Set<String>,
     onDelete: (DownloadedFile) -> Unit,
     onCancel: (ActiveDownload) -> Unit,
     onUpload: (DownloadedFile) -> Unit,
@@ -214,7 +216,13 @@ fun DownloadsScreen(
                             verticalAlignment = Alignment.CenterVertically
                         ) {
                             Column(Modifier.weight(1f)) {
-                                Text(file.name, style = MaterialTheme.typography.bodyMedium, fontWeight = FontWeight.Medium, maxLines = 1, overflow = TextOverflow.Ellipsis)
+                                Row(verticalAlignment = Alignment.CenterVertically) {
+                                    Text(file.name, style = MaterialTheme.typography.bodyMedium, fontWeight = FontWeight.Medium, maxLines = 1, overflow = TextOverflow.Ellipsis, modifier = Modifier.weight(1f, fill = false))
+                                    if (file.name in uploadedNames) {
+                                        Spacer(Modifier.width(6.dp))
+                                        Icon(Icons.Filled.CloudDone, "On server", tint = MaterialTheme.colorScheme.primary, modifier = Modifier.size(16.dp))
+                                    }
+                                }
                                 Text(formatSize(file.size), style = MaterialTheme.typography.bodySmall, color = MaterialTheme.colorScheme.onSurfaceVariant)
                             }
                             if (isDeleting) {

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

@@ -62,6 +62,7 @@ fun YarisMainScreen(client: OkHttpClient) {
     val activeDownloads by dashcamVm.activeDownloads.collectAsState()
     val deletingNames by dashcamVm.deletingNames.collectAsState()
     val uploadProgress by dashcamVm.uploadProgress.collectAsState()
+    val uploadedNames by dashcamVm.uploadedNames.collectAsState()
     val dashcamFiles by dashcamVm.dashcamFiles.collectAsState()
     val dashcamTotalSize by dashcamVm.dashcamTotalSize.collectAsState()
     val dashcamStatus by dashcamVm.dashcamStatus.collectAsState()
@@ -129,6 +130,7 @@ fun YarisMainScreen(client: OkHttpClient) {
                     activeUploads = uploadProgress,
                     deletingNames = deletingNames,
                     credentialsConfigured = credentialsConfigured,
+                    uploadedNames = uploadedNames,
                     onDelete = { dashcamVm.deleteDownloaded(it) },
                     onCancel = { dashcamVm.cancelDownload(it) },
                     onUpload = { dashcamVm.uploadFile(it) },

android/app/src/main/java/com/yarisobd/app/data/CredentialStore.kt

@@ -7,6 +7,7 @@ object CredentialStore {
     private const val KEY_SERVER_URL = "server_url"
     private const val KEY_DEVICE_NAME = "device_name"
     private const val KEY_API_KEY = "api_key"
+    private const val KEY_UPLOADED = "uploaded_files"
 
     private fun prefs(context: Context) =
         context.getSharedPreferences(PREFS, Context.MODE_PRIVATE)
@@ -25,4 +26,13 @@ object CredentialStore {
             .putString(KEY_API_KEY, apiKey)
             .apply()
     }
+
+    fun markUploaded(context: Context, filename: String) {
+        val set = getUploaded(context).toMutableSet()
+        set.add(filename)
+        prefs(context).edit().putStringSet(KEY_UPLOADED, set).apply()
+    }
+
+    fun getUploaded(context: Context): Set<String> =
+        prefs(context).getStringSet(KEY_UPLOADED, emptySet()) ?: emptySet()
 }