chore: eliminate all Kotlin compiler warnings in main source (#877)

* chore: eliminate all Kotlin compiler warnings in main source

* test(chat): fix cross-class coroutine leaks poisoning the unit suite

- ChatUpdateCommandTest: inject FakeSlashUsageStore — the real DataStore
  store inits on real IO threads with a relaxed-mock app (cacheDir NPE)
  and leaks an uncaught exception into the next runTest class.
- ChatUpdateCommandTest + SlashCommandDispatchRpcTest: mock
  ProfileSwitchCoordinator.switched (ChatViewModelTest pattern) — VMs
  otherwise park collectors on the singleton flow that crash later
  classes (ProfileSwitchCoordinatorTest) on stale-Main resumption.

Full suite: 944 tests, 0 failures (was 2 flaky per run).

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

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

@@ -94,8 +94,8 @@ class MainActivity : ComponentActivity() {
         // Issue #832: MainActivity is exported (launcher requirement) — only
         // honor intents stamped with our own notification action.
         if (intent?.action != ACTION_OPEN_CHAT_FROM_NOTIFICATION) return
-        val sessionId = intent?.getStringExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
-        intent?.removeExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
+        val sessionId = intent.getStringExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
+        intent.removeExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
         sessionId?.takeIf { it.isNotBlank() }?.let(NavigationController::openChatSession)
     }
 }