Handle account switch in RootFlowNode instead of in presenters

PreferencesRootPresenter and HomePresenter were updating the latest session
in the session store directly, relying on RootNavStateFlow to trigger the
navigation as a side effect. Changing the current session is app-level
navigation, so it is now forwarded through a new `navigateToSession` callback
up to RootFlowNode, which performs the session store update.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

appnav/src/main/kotlin/io/element/android/appnav/LoggedInAppScopeFlowNode.kt

@@ -33,6 +33,7 @@ import io.element.android.libraries.architecture.createNode
 import io.element.android.libraries.architecture.inputs
 import io.element.android.libraries.di.DependencyInjectionGraphOwner
 import io.element.android.libraries.matrix.api.MatrixClient
+import io.element.android.libraries.matrix.api.core.SessionId
 import io.element.android.libraries.matrixmedia.api.ImageLoaderHolder
 import kotlinx.parcelize.Parcelize
 
@@ -59,6 +60,7 @@ class LoggedInAppScopeFlowNode(
     interface Callback : Plugin {
         fun navigateToBugReport()
         fun navigateToAddAccount()
+        fun navigateToSession(sessionId: SessionId)
     }
 
     private val callback: Callback = callback()
@@ -91,6 +93,10 @@ class LoggedInAppScopeFlowNode(
             override fun navigateToAddAccount() {
                 callback.navigateToAddAccount()
             }
+
+            override fun navigateToSession(sessionId: SessionId) {
+                callback.navigateToSession(sessionId)
+            }
         }
         return createNode<LoggedInFlowNode>(buildContext, listOf(callback))
     }

appnav/src/main/kotlin/io/element/android/appnav/LoggedInFlowNode.kt

@@ -85,6 +85,7 @@ import io.element.android.libraries.matrix.api.MatrixClient
 import io.element.android.libraries.matrix.api.core.EventId
 import io.element.android.libraries.matrix.api.core.RoomId
 import io.element.android.libraries.matrix.api.core.RoomIdOrAlias
+import io.element.android.libraries.matrix.api.core.SessionId
 import io.element.android.libraries.matrix.api.core.UserId
 import io.element.android.libraries.matrix.api.core.toRoomIdOrAlias
 import io.element.android.libraries.matrix.api.permalink.PermalinkData
@@ -169,6 +170,7 @@ class LoggedInFlowNode(
     interface Callback : Plugin {
         fun navigateToBugReport()
         fun navigateToAddAccount()
+        fun navigateToSession(sessionId: SessionId)
     }
 
     private val callback: Callback = callback()
@@ -356,6 +358,10 @@ class LoggedInFlowNode(
                     override fun navigateToAddAccount() {
                         callback.navigateToAddAccount()
                     }
+
+                    override fun navigateToSession(sessionId: SessionId) {
+                        callback.navigateToSession(sessionId)
+                    }
                 }
                 homeEntryPoint.createNode(
                     parentNode = this,
@@ -448,6 +454,10 @@ class LoggedInFlowNode(
                         callback.navigateToAddAccount()
                     }
 
+                    override fun navigateToSession(sessionId: SessionId) {
+                        callback.navigateToSession(sessionId)
+                    }
+
                     override fun navigateToLinkNewDevice() {
                         backstack.push(NavTarget.LinkNewDevice)
                     }

appnav/src/main/kotlin/io/element/android/appnav/RootFlowNode.kt

@@ -416,6 +416,12 @@ class RootFlowNode(
                     override fun navigateToAddAccount() {
                         backstack.push(NavTarget.NotLoggedInFlow(null))
                     }
+
+                    override fun navigateToSession(sessionId: SessionId) {
+                        lifecycleScope.launch {
+                            sessionStore.setLatestSession(sessionId.value)
+                        }
+                    }
                 }
                 val savedNavState = extractSavedStateForNavTarget(navTarget, this.buildContext.savedStateMap)
                 val buildContext = if (savedNavState != null) {