feat(#76): add testTag identifiers to composable elements for UI test targeting (#98)

Adds testTag modifiers to key interactive elements across the core
composables, enabling Espresso/Compose UI tests to locate them:

Navigation.kt  — 'nav_*' on bottom bar items, 'drawer_*' on drawer items
HermesScaffold — 'back_button', 'menu_button', 'refresh_button'
StateViews.kt  — 'loading_state', 'loading_spinner', 'error_retry_button',
                 'empty_state_action'
ChatScreen.kt  — 'chat_input', 'send_button', 'interrupt_button'

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/Navigation.kt

@@ -56,6 +56,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.vector.ImageVector
+import androidx.compose.ui.platform.testTag
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.navigation3.runtime.NavKey
@@ -279,7 +280,10 @@ fun MainNavigation() {
                                             selectedTextColor = MaterialTheme.colorScheme.onPrimaryContainer,
                                             selectedIconColor = MaterialTheme.colorScheme.onPrimaryContainer,
                                         ),
-                                    modifier = Modifier.padding(horizontal = 12.dp, vertical = 2.dp),
+                                    modifier =
+                                        Modifier
+                                            .padding(horizontal = 12.dp, vertical = 2.dp)
+                                            .testTag("drawer_${entry.label.lowercase().replace(' ', '_')}"),
                                 )
                             }
                     }
@@ -302,6 +306,7 @@ fun MainNavigation() {
                                 onClick = { NavigationController.navigateTo(item.key) },
                                 icon = { Icon(item.icon, contentDescription = item.label) },
                                 label = { Text(item.label) },
+                                modifier = Modifier.testTag("nav_${item.label.lowercase().replace(' ', '_')}"),
                             )
                         }
                     }