feat: add newsletter toggle in Settings screen

- Add "Newsletter" section after Content/Tags section
- Switch to enable/disable newsletter features per account
- Info text explaining the toggle's effect on composer
- Best-effort API validation when toggling ON (fetches newsletters count)
- Animated validation status display

app/src/main/java/com/swoosh/microblog/ui/settings/SettingsScreen.kt

@@ -32,8 +32,11 @@ import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import coil.compose.AsyncImage
 import com.swoosh.microblog.data.AccountManager
+import com.swoosh.microblog.data.NewsletterPreferences
 import com.swoosh.microblog.data.SiteMetadataCache
 import com.swoosh.microblog.data.api.ApiClient
+import com.swoosh.microblog.data.repository.PostRepository
+import kotlinx.coroutines.launch
 import com.swoosh.microblog.data.model.GhostAccount
 import com.swoosh.microblog.ui.animation.SwooshMotion
 import com.swoosh.microblog.ui.components.ConfirmationDialog
@@ -293,6 +296,13 @@ fun SettingsScreen(
             HorizontalDivider()
             Spacer(modifier = Modifier.height(24.dp))
 
+            // --- Newsletter section ---
+            NewsletterSettingsSection()
+
+            Spacer(modifier = Modifier.height(24.dp))
+            HorizontalDivider()
+            Spacer(modifier = Modifier.height(24.dp))
+
             // --- Current Account section ---
             Text("Current Account", style = MaterialTheme.typography.titleMedium)
             Spacer(modifier = Modifier.height(12.dp))
@@ -444,6 +454,86 @@ fun SettingsScreen(
     }
 }
 
+@Composable
+fun NewsletterSettingsSection() {
+    val context = LocalContext.current
+    val newsletterPreferences = remember { NewsletterPreferences(context) }
+    var newsletterEnabled by remember { mutableStateOf(newsletterPreferences.isNewsletterEnabled()) }
+    val coroutineScope = rememberCoroutineScope()
+    var validationStatus by remember { mutableStateOf<String?>(null) }
+
+    Text("Newsletter", style = MaterialTheme.typography.titleMedium)
+    Spacer(modifier = Modifier.height(12.dp))
+
+    Card(modifier = Modifier.fillMaxWidth()) {
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(16.dp)
+        ) {
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                horizontalArrangement = Arrangement.SpaceBetween,
+                verticalAlignment = Alignment.CenterVertically
+            ) {
+                Column(modifier = Modifier.weight(1f)) {
+                    Text(
+                        text = "Enable newsletter features",
+                        style = MaterialTheme.typography.bodyLarge
+                    )
+                }
+                Switch(
+                    checked = newsletterEnabled,
+                    onCheckedChange = { enabled ->
+                        newsletterEnabled = enabled
+                        newsletterPreferences.setNewsletterEnabled(enabled)
+                        if (enabled) {
+                            // Best effort: validate by fetching newsletters
+                            validationStatus = "Checking..."
+                            coroutineScope.launch {
+                                try {
+                                    val repository = PostRepository(context)
+                                    val result = repository.fetchNewsletters()
+                                    validationStatus = if (result.isSuccess) {
+                                        val count = result.getOrNull()?.size ?: 0
+                                        "$count newsletter(s) found"
+                                    } else {
+                                        null
+                                    }
+                                } catch (_: Exception) {
+                                    validationStatus = null
+                                }
+                            }
+                        } else {
+                            validationStatus = null
+                        }
+                    }
+                )
+            }
+
+            Text(
+                text = "Show newsletter sending options when publishing posts",
+                style = MaterialTheme.typography.bodySmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant
+            )
+
+            // Validation status
+            AnimatedVisibility(
+                visible = validationStatus != null,
+                enter = fadeIn(SwooshMotion.quick()) + expandVertically(animationSpec = SwooshMotion.snappy()),
+                exit = fadeOut(SwooshMotion.quick()) + shrinkVertically(animationSpec = SwooshMotion.snappy())
+            ) {
+                Text(
+                    text = validationStatus ?: "",
+                    style = MaterialTheme.typography.labelSmall,
+                    color = MaterialTheme.colorScheme.primary,
+                    modifier = Modifier.padding(top = 4.dp)
+                )
+            }
+        }
+    }
+}
+
 @Composable
 fun ThemeModeSelector(
     currentMode: ThemeMode,