refactor: use injected ioDispatcher and ApplicationCoroutineScope

Replaces two coroutine anti-patterns flagged by the architecture audit:

* FirmwareUpdateViewModel.onCleared() was using GlobalScope.launch to
  run cleanup work that must outlive the ViewModel scope. Introduce a
  new ApplicationCoroutineScope marker interface + Koin @Single binding
  in core/common, backed by SupervisorJob() + ioDispatcher, and inject
  it into the VM. NonCancellable is preserved so shutdown work still
  cannot be interrupted. Verified end-to-end by the KoinVerificationTest
  full-graph check.
* Six sites in feature/settings (android+jvm LogExporter/PrefExporter)
  and core/ui (android+jvm PlatformUtils) were hardcoding Dispatchers.IO.
  Switch to the project's injectable ioDispatcher property so tests
  can substitute a test dispatcher without reflection.

Dispatchers.Main sites in LogExporter are intentionally left alone —
they are fully test-swappable via Dispatchers.setMain() and there is
no existing mainDispatcher property to inject.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

feature/firmware/src/commonMain/kotlin/org/meshtastic/feature/firmware/FirmwareUpdateViewModel.kt

@@ -35,6 +35,7 @@ import kotlinx.coroutines.launch
 import kotlinx.coroutines.withTimeoutOrNull
 import org.jetbrains.compose.resources.StringResource
 import org.koin.core.annotation.KoinViewModel
+import org.meshtastic.core.common.di.ApplicationCoroutineScope
 import org.meshtastic.core.common.util.CommonUri
 import org.meshtastic.core.common.util.safeCatching
 import org.meshtastic.core.database.entity.FirmwareRelease
@@ -91,6 +92,7 @@ class FirmwareUpdateViewModel(
     private val firmwareUpdateManager: FirmwareUpdateManager,
     private val usbManager: FirmwareUsbManager,
     private val fileHandler: FirmwareFileHandler,
+    private val applicationScope: ApplicationCoroutineScope,
 ) : ViewModel() {
 
     private val _state = MutableStateFlow<FirmwareUpdateState>(FirmwareUpdateState.Idle)
@@ -124,12 +126,10 @@ class FirmwareUpdateViewModel(
 
     override fun onCleared() {
         super.onCleared()
-        // viewModelScope is already cancelled when onCleared() runs, so launch cleanup in a
-        // standalone scope. SupervisorJob prevents the coroutine from propagating failures to a
-        // shared parent, and NonCancellable on the launch keeps cleanup running even if the scope
-        // is cancelled concurrently.
-        @OptIn(kotlinx.coroutines.DelicateCoroutinesApi::class)
-        kotlinx.coroutines.GlobalScope.launch(NonCancellable) {
+        // viewModelScope is already cancelled when onCleared() runs, so launch cleanup on the
+        // application-wide scope (SupervisorJob + ioDispatcher). NonCancellable keeps cleanup
+        // running even if something tries to cancel it mid-flight.
+        applicationScope.launch(NonCancellable) {
             tempFirmwareFile = cleanupTemporaryFiles(fileHandler, tempFirmwareFile)
         }
     }

feature/firmware/src/commonTest/kotlin/org/meshtastic/feature/firmware/FirmwareUpdateIntegrationTest.kt

@@ -108,6 +108,7 @@ class FirmwareUpdateIntegrationTest {
         firmwareUpdateManager,
         usbManager,
         fileHandler,
+        TestApplicationCoroutineScope(testDispatcher),
     )
 
     @Test

feature/firmware/src/commonTest/kotlin/org/meshtastic/feature/firmware/FirmwareUpdateViewModelTest.kt

@@ -124,6 +124,7 @@ class FirmwareUpdateViewModelTest {
         firmwareUpdateManager,
         usbManager,
         fileHandler,
+        TestApplicationCoroutineScope(testDispatcher),
     )
 
     @Test

feature/firmware/src/commonTest/kotlin/org/meshtastic/feature/firmware/TestApplicationCoroutineScope.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.feature.firmware
+
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.SupervisorJob
+import org.meshtastic.core.common.di.ApplicationCoroutineScope
+
+internal class TestApplicationCoroutineScope(dispatcher: CoroutineDispatcher) :
+    ApplicationCoroutineScope,
+    CoroutineScope by CoroutineScope(SupervisorJob() + dispatcher)

feature/firmware/src/jvmTest/kotlin/org/meshtastic/feature/firmware/FirmwareUpdateViewModelFileTest.kt

@@ -116,6 +116,7 @@ class FirmwareUpdateViewModelFileTest {
         firmwareUpdateManager,
         usbManager,
         fileHandler,
+        TestApplicationCoroutineScope(testDispatcher),
     )
 
     // -----------------------------------------------------------------------