Ignore Office lock files

Word creates ~$<name>.docx beside a document while it is open and removes it on
close. docs/~$crOBU-User-Guide.docx was showing as untracked while the user guide
was being edited, which is exactly the kind of transient file a git add -A sweeps
in by accident.

.gitignore

@@ -38,3 +38,7 @@ sdkconfig.old
 # Third-party working copies kept beside the project, not part of it. The ASN.1
 # modules this project actually needs are vendored under asn1/ instead.
 /C-ITS-Parser/
+
+# Office lock files. Word/Excel create these beside a document while it is open
+# and remove them on close, so they are transient and machine-local.
+~$*

app/src/main/java/com/hawhamburg/micr0bu/ui/navigation/AppNavigation.kt

@@ -63,6 +63,23 @@ private val bottomNavItems = listOf(
     Screen.Settings,
 )
 
+/**
+ * True if [route] is this tab's own screen or one of its sub-screens.
+ *
+ * The graph is flat, so ownership is derived from the route naming convention: every Settings
+ * sub-screen is "settings/...", and a trip review is "trip_review/{tripId}" belonging to Trips.
+ * Without this, a tab stops looking selected the moment you open anything inside it.
+ */
+private fun Screen.ownsRoute(route: String?): Boolean {
+    if (route == null) return false
+    if (route == this.route) return true
+    return when (this) {
+        Screen.Settings    -> route.startsWith("settings/")
+        Screen.TripHistory -> route.startsWith("trip_review")
+        else               -> false
+    }
+}
+
 @Composable
 fun BottomNavBar(navController: NavController) {
     val backStackEntry by navController.currentBackStackEntryAsState()
@@ -70,13 +87,24 @@ fun BottomNavBar(navController: NavController) {
 
     NavigationBar {
         bottomNavItems.forEach { screen ->
+            val onThisTab = screen.ownsRoute(currentRoute)
             NavigationBarItem(
-                selected = currentRoute == screen.route,
+                selected = onThisTab,
                 onClick = {
-                    navController.navigate(screen.route) {
-                        popUpTo(Screen.Dashboard.route) { saveState = true }
-                        launchSingleTop = true
-                        restoreState = true
+                    if (onThisTab && currentRoute != screen.route) {
+                        // Already inside this tab, just deeper in: pop back to the tab's own
+                        // screen. Navigating instead would restoreState the saved back stack and
+                        // land straight back on the sub-screen, which reads as the tap doing
+                        // nothing - the reason Settings > Connection could not be left by tapping
+                        // Settings. Leaves the rest of the stack intact, so Back still works
+                        // exactly as before.
+                        navController.popBackStack(screen.route, inclusive = false)
+                    } else {
+                        navController.navigate(screen.route) {
+                            popUpTo(Screen.Dashboard.route) { saveState = true }
+                            launchSingleTop = true
+                            restoreState = true
+                        }
                     }
                 },
                 icon = {