feat: Material icons in nav bar + yaris-obd header on all screens

- Tab icons: Icons.Filled.Videocam / FileDownload / Settings
- Branding header (yaris-obd + Phase 28 subtitle) on Dashcam, Downloads, Settings

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

@@ -50,7 +50,21 @@ fun DashcamScreen(
     onDelete: (VideoFile) -> Unit,
 ) {
     Column(modifier = Modifier.fillMaxSize()) {
-        // Header
+        // Branding header
+        Text(
+            "yaris-obd",
+            style = MaterialTheme.typography.headlineLarge,
+            color = MaterialTheme.colorScheme.primary,
+            modifier = Modifier.padding(start = 16.dp, top = 8.dp)
+        )
+        Text(
+            "Phase 28 — Android Companion",
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            modifier = Modifier.padding(start = 16.dp)
+        )
+
+        // Header card
         Card(
             modifier = Modifier
                 .fillMaxWidth()

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

@@ -65,7 +65,21 @@ fun DownloadsScreen(
     val context = LocalContext.current
 
     Column(modifier = Modifier.fillMaxSize()) {
-        // Header
+        // Branding header
+        Text(
+            "yaris-obd",
+            style = MaterialTheme.typography.headlineLarge,
+            color = MaterialTheme.colorScheme.primary,
+            modifier = Modifier.padding(start = 16.dp, top = 8.dp)
+        )
+        Text(
+            "Phase 28 — Android Companion",
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            modifier = Modifier.padding(start = 16.dp)
+        )
+
+        // Header card
         Card(
             modifier = Modifier.fillMaxWidth().padding(16.dp),
             colors = CardDefaults.cardColors(containerColor = MaterialTheme.colorScheme.surfaceContainerHigh)

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

@@ -8,6 +8,7 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Icon
+import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.NavigationBar
 import androidx.compose.material3.NavigationBarItem
@@ -15,6 +16,10 @@ import androidx.compose.material3.Scaffold
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Text
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Videocam
+import androidx.compose.material.icons.filled.FileDownload
+import androidx.compose.material.icons.filled.Settings
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
@@ -77,19 +82,19 @@ fun YarisMainScreen(client: OkHttpClient) {
                 NavigationBarItem(
                     selected = selectedTab == 0,
                     onClick = { selectedTab = 0 },
-                    icon = { Text("Cam") },
+                    icon = { Icon(Icons.Filled.Videocam, contentDescription = "Dashcam") },
                     label = { Text("Dashcam") }
                 )
                 NavigationBarItem(
                     selected = selectedTab == 1,
                     onClick = { selectedTab = 1 },
-                    icon = { Text("DL") },
+                    icon = { Icon(Icons.Filled.FileDownload, contentDescription = "Downloads") },
                     label = { Text("Downloads") }
                 )
                 NavigationBarItem(
                     selected = selectedTab == 2,
                     onClick = { selectedTab = 2 },
-                    icon = { Text("Set") },
+                    icon = { Icon(Icons.Filled.Settings, contentDescription = "Settings") },
                     label = { Text("Settings") }
                 )
             }