fix: move public trust caption to a localized caption band (#1064)

Ask 6 — SE-width header overflow: the mesh trust caption lived as a
`.fixedSize(horizontal: true)` `Text` inside the header's trailing
`.layoutPriority(3)` (non-compressible) cluster, so on a narrow (SE-width)
header it forced the row to overflow. Relocated it out of the header into a
persistent full-width caption band under the public timeline — the parity twin
of the DM sheet's `privacyCaption` band (#1366): same structure (full width,
`.themedSurface()`, centered, combined a11y), rendered above the composer in
both the glass and matrix layouts, mesh-only (geohash/location channels carry no
such caption). It is muted (`palette.secondary`), not orange, because orange is
the DM privacy signal and this surface is deliberately public. `ContentView`
gains `locationChannelsModel` (already injected on its environment in
`BitchatApp`) to gate the mesh condition.

Ask 7 — untranslatable hardcoded vocabulary: the caption and its accessibility
label were `Text(verbatim:)` literals ("public · unencrypted" / "public,
unencrypted") that bypassed `Localizable.xcstrings`. Replaced with two new
localized keys — `content.header.public_caption` ("public · nearby", visible,
`·` separator matching the DM caption band's "private · end-to-end encrypted")
and `content.header.public_caption.a11y` ("public, nearby", VoiceOver, comma
form). Both reuse the established public-surface vocabulary from #1357's
`content.input.placeholder.mesh` ("… public, nearby") rather than coining a new
"unencrypted" string. Only the `en` source value is seeded; other locales are
left for translators, matching the existing DM-caption keys.

NOT locally compiled (Swift/iOS; CI runs Build iOS + Swift Tests). Visual
placement/spacing of the new band is unverified — needs an SE-width eyeball.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bitchat/Localizable.xcstrings

@@ -18051,6 +18051,30 @@
         }
       }
     },
+    "content.header.public_caption" : {
+      "comment" : "Trust caption under the public mesh timeline: this channel is public and reaches nearby devices. Reuses the composer placeholder vocabulary (content.input.placeholder.mesh).",
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "public · nearby"
+          }
+        }
+      }
+    },
+    "content.header.public_caption.a11y" : {
+      "comment" : "Accessibility label for the public mesh trust caption; comma form of content.header.public_caption for VoiceOver.",
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "public, nearby"
+          }
+        }
+      }
+    },
     "content.help.verification" : {
       "extractionState" : "manual",
       "localizations" : {

bitchat/Views/ContentHeaderView.swift

@@ -186,15 +186,6 @@ struct ContentHeaderView: View {
                 }
                 .buttonStyle(.plain)
 
-                if case .mesh = locationChannelsModel.selectedChannel {
-                    Text(verbatim: "public · unencrypted")
-                        .bitchatFont(size: 10)
-                        .foregroundColor(palette.secondary)
-                        .lineLimit(1)
-                        .fixedSize(horizontal: true, vertical: false)
-                        .accessibilityLabel(Text(verbatim: "public, unencrypted"))
-                }
-
                 Button(action: {
                     withAnimation(.easeInOut(duration: TransportConfig.uiAnimationMediumSeconds)) {
                         showSidebar.toggle()

bitchat/Views/ContentView.swift

@@ -35,6 +35,7 @@ struct ContentView: View {
     @EnvironmentObject private var privateConversationModel: PrivateConversationModel
     @EnvironmentObject private var verificationModel: VerificationModel
     @EnvironmentObject private var conversationUIModel: ConversationUIModel
+    @EnvironmentObject private var locationChannelsModel: LocationChannelsModel
 
     @StateObject private var voiceRecordingVM = VoiceRecordingViewModel()
     @State private var messageText = ""
@@ -239,7 +240,10 @@ struct ContentView: View {
                 }
                 .safeAreaInset(edge: .bottom, spacing: 0) {
                     if selectedPrivatePeerID == nil {
-                        composerView
+                        VStack(spacing: 0) {
+                            meshPrivacyCaption
+                            composerView
+                        }
                     }
                 }
         } else {
@@ -260,12 +264,32 @@ struct ContentView: View {
                 Divider()
 
                 if selectedPrivatePeerID == nil {
+                    meshPrivacyCaption
                     composerView
                 }
             }
         }
     }
 
+    /// Persistent trust caption under the PUBLIC mesh timeline — the parity
+    /// twin of the DM sheet's `privacyCaption` (#1366). Moved here out of the
+    /// header's non-compressible trailing cluster, where its `.fixedSize` text
+    /// overflowed narrow (SE-width) headers. Mesh-only: geohash/location
+    /// channels carry no such caption. Muted rather than orange — orange is the
+    /// DM privacy signal; this surface is deliberately public.
+    @ViewBuilder
+    private var meshPrivacyCaption: some View {
+        if case .mesh = locationChannelsModel.selectedChannel {
+            Text("content.header.public_caption")
+                .bitchatFont(size: 11, weight: .medium)
+                .foregroundColor(palette.secondary)
+                .frame(maxWidth: .infinity)
+                .padding(.vertical, 4)
+                .themedSurface()
+                .accessibilityLabel(Text("content.header.public_caption.a11y"))
+        }
+    }
+
     private var headerView: some View {
         ContentHeaderView(
             showSidebar: $appChromeModel.showSidebar,