Refactor: Extract RootScreen from MainActivity and fix reply message user

This commit refactors the UI composition logic by extracting it from `MainActivity` into a new, dedicated `RootScreen` composable. This improves the separation of concerns and simplifies `MainActivity`.

Additionally, a bug has been fixed where a replied-to message would incorrectly display the author of the parent message instead of its own author.

Key changes:
- Moved theme setup, permission handling, Long-Poll/Online service management, and navigation graph hosting into the new `RootScreen.kt`.
- `MainActivity` is now significantly simplified, delegating its UI composition to `RootScreen`.
- Corrected the user and group assignment for `replyMessage` in `MessagesRepositoryImpl` to ensure the correct author is displayed.
- Introduced `OnlineFriendsViewModel` to the `FriendsRoute` to separate the logic for online friends.
- Replaced `List` with a custom `ImmutableList` for `photoViewerInfo` state to improve Compose stability.

feature/messageshistory/src/main/kotlin/dev/meloda/fast/messageshistory/model/UiItem.kt

@@ -1,5 +1,6 @@
 package dev.meloda.fast.messageshistory.model
 
+import androidx.compose.runtime.Stable
 import androidx.compose.ui.text.AnnotatedString
 import dev.meloda.fast.common.model.UiImage
 import dev.meloda.fast.model.api.domain.VkAttachment
@@ -9,6 +10,7 @@ sealed class UiItem(
     open val cmId: Long
 ) {
 
+    @Stable
     data class Message(
         override val id: Long,
         override val cmId: Long,
@@ -35,6 +37,7 @@ sealed class UiItem(
         val replySummary: String?
     ) : UiItem(id, cmId)
 
+    @Stable
     data class ActionMessage(
         override val id: Long,
         override val cmId: Long,