feat: portal-wide device selector — session-based, all pages now use selected device

- _portal_device_id() reads from session, falls back to DEVICE_NAME env var
- GET/POST /api/v1/portal/select-device for selector data + set
- Dropdown in server base.html topbar, JS populates from API, page reloads on change
- All portal pages (overview, trips, dashcam, DTC, device settings) now use selected device

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

@@ -21,6 +21,7 @@ import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.LinearProgressIndicator
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
@@ -43,6 +44,7 @@ fun DashcamScreen(
     retentionDays: Int,
     isLoading: Boolean,
     error: String?,
+    downloadProgress: Map<String, DownloadProgress>,
     onRefresh: () -> Unit,
     onDownload: (VideoFile) -> Unit,
     onDelete: (VideoFile) -> Unit,
@@ -146,8 +148,10 @@ fun DashcamScreen(
                     verticalArrangement = Arrangement.spacedBy(8.dp)
                 ) {
                     items(videos, key = { it.path }) { video ->
+                        val progress = downloadProgress[video.path]
                         VideoRow(
                             video = video,
+                            downloadProgress = progress,
                             onDownload = { onDownload(video) },
                             onDelete = { onDelete(video) },
                         )
@@ -161,6 +165,7 @@ fun DashcamScreen(
 @Composable
 private fun VideoRow(
     video: VideoFile,
+    downloadProgress: DownloadProgress?,
     onDownload: () -> Unit,
     onDelete: () -> Unit,
 ) {
@@ -224,6 +229,20 @@ private fun VideoRow(
                         style = MaterialTheme.typography.bodySmall,
                         color = MaterialTheme.colorScheme.tertiary
                     )
+                } else if (downloadProgress != null) {
+                    LinearProgressIndicator(
+                        progress = {
+                            if (downloadProgress.totalBytes > 0)
+                                downloadProgress.bytesDownloaded.toFloat() / downloadProgress.totalBytes
+                            else 0f
+                        },
+                        modifier = Modifier.fillMaxWidth().padding(top = 4.dp),
+                    )
+                    Text(
+                        text = "Downloading ${downloadProgress.bytesDownloaded / 1_000_000}MB / ${downloadProgress.totalBytes / 1_000_000}MB",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.primary
+                    )
                 } else {
                     Text(
                         text = if (video.uploaded) "Uploaded" else "Pending",