Feature/screenshot privacy warning (#541)

* Screenshot privacy: warn on location sheet; gate screenshot broadcasts to chat only\n\n- Track sheet presentation in ChatViewModel\n- Show privacy alert when screenshot taken on location channels\n- Ignore screenshots for App Info and Location sheet for broadcast\n- ContentView wires sheet onAppear/onDisappear and presents alert\n- Fix location sheet subtitle wrapping: render as single Text to avoid orphaned bullets

* Fix duplicate messages after channel switch\n\n- Dedup on per-geohash append (skip if ID exists)\n- Dedup and sort timeline by timestamp when switching into a geohash\n- Keep content/layout unchanged; add lightweight debug logs for empty rows

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Views/ContentView.swift

@@ -165,6 +165,8 @@ struct ContentView: View {
         }
         .sheet(isPresented: $showAppInfo) {
             AppInfoView()
+                .onAppear { viewModel.isAppInfoPresented = true }
+                .onDisappear { viewModel.isAppInfoPresented = false }
         }
         .sheet(isPresented: Binding(
             get: { viewModel.showingFingerprintFor != nil },
@@ -279,8 +281,10 @@ struct ContentView: View {
                         }
                     }()
                     let items = windowedMessages.map { (uiID: "\(contextKey)|\($0.id)", message: $0) }
-                    
-                    ForEach(items, id: \.uiID) { item in
+                    // Filter out empty/whitespace-only messages to avoid blank rows
+                    let filteredItems = items.filter { !$0.message.content.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty }
+
+                    ForEach(filteredItems, id: \.uiID) { item in
                         let message = item.message
                         VStack(alignment: .leading, spacing: 0) {
                             // Check if current user is mentioned
@@ -1182,6 +1186,13 @@ struct ContentView: View {
         .padding(.horizontal, 12)
         .sheet(isPresented: $showLocationChannelsSheet) {
             LocationChannelsSheet(isPresented: $showLocationChannelsSheet)
+                .onAppear { viewModel.isLocationChannelsSheetPresented = true }
+                .onDisappear { viewModel.isLocationChannelsSheetPresented = false }
+        }
+        .alert("heads up", isPresented: $viewModel.showScreenshotPrivacyWarning) {
+            Button("ok", role: .cancel) {}
+        } message: {
+            Text("screenshots of location channels will reveal your location. think before sharing publicly.")
         }
         .background(backgroundColor.opacity(0.95))
     }