fix(#214): notification tap now navigates to correct session

Root cause: MainActivity had no onNewIntent override. When the app was
backgrounded and a notification was tapped, Android brought the existing
task to the foreground and delivered the intent via onNewIntent — but
since it wasn't overridden, the session ID from the notification was
silently dropped and the user saw the last-active session.

Fix:
1. Changed notificationSessionId from a local val to a Compose
   mutableStateOf so it's observable across recompositions.
2. Added onNewIntent override that reads the session ID from the
   incoming intent and updates the observable state.
3. Added FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP to the
   notification PendingIntent for reliable task management.

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

@@ -1,5 +1,6 @@
 package com.m57.hermescontrol
 
+import android.content.Intent
 import android.os.Bundle
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
@@ -9,17 +10,21 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.ui.Modifier
 import com.m57.hermescontrol.data.local.AuthManager
 import com.m57.hermescontrol.notification.NotificationReplyReceiver
 import com.m57.hermescontrol.theme.HermesControlTheme
 
 class MainActivity : ComponentActivity() {
+    // Observable state so both onCreate and onNewIntent updates flow to Compose
+    private var notificationSessionId by mutableStateOf<String?>(null)
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
         // Read notification tap sessionId (if any) from the intent that launched us
-        val notificationSessionId = intent?.getStringExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
+        notificationSessionId = intent?.getStringExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
 
         enableEdgeToEdge()
         setContent {
@@ -40,4 +45,13 @@ class MainActivity : ComponentActivity() {
             }
         }
     }
+
+    override fun onNewIntent(intent: Intent) {
+        super.onNewIntent(intent)
+        // When a notification tap arrives while the app is already running
+        // (task exists in background), Android delivers the intent here instead
+        // of onCreate. Update the observable state so Compose recomposes
+        // and ChatScreen's LaunchedEffect switches to the correct session.
+        notificationSessionId = intent.getStringExtra(NotificationReplyReceiver.EXTRA_SESSION_ID)
+    }
 }

app/src/main/java/com/m57/hermescontrol/notification/ChatNotificationService.kt

@@ -153,9 +153,11 @@ class ChatNotificationService : Service() {
     }
 
     private fun buildContentIntent(sessionId: String?): PendingIntent {
-        val intent = Intent(this, MainActivity::class.java)
-        if (!sessionId.isNullOrBlank()) {
-            intent.putExtra(NotificationReplyReceiver.EXTRA_SESSION_ID, sessionId)
+        val intent = Intent(this, MainActivity::class.java).apply {
+            flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TOP
+            if (!sessionId.isNullOrBlank()) {
+                putExtra(NotificationReplyReceiver.EXTRA_SESSION_ID, sessionId)
+            }
         }
         return PendingIntent.getActivity(
             this,