Give private DMs an unmistakable visual signature (#1357)

* Give private DMs an unmistakable visual signature

An open DM renders identically to the public room — same view, same
green-on-black surface, with a small header name and two orange icons
as the only cues. For this audience the cost of misreading "am I in the
encrypted DM or the public channel?" is severe: sensitive text typed
into the wrong composer.

Four presentation-layer cues; no formatter or cache changes:

- The composer placeholder states the destination instead of a generic
  prompt: "message @jack — private" in a DM, "message #mesh — public,
  nearby" on mesh, "message #9q8yy — public" in a geohash channel.
- A persistent lock caption sits above the DM composer. It reads
  "private · end-to-end encrypted" only once the Noise session is
  actually secured or verified, and "private conversation" before that
  — the caption must not overstate encryption mid-handshake.
- The DM sheet header carries a faint orange wash (6%), extending the
  existing orange self-accent to the chrome.
- Each private message row is prefixed with a small orange lock glyph
  (view-layer, hidden from VoiceOver — the caption carries the
  semantic; the cached AttributedString formatter is untouched).

New strings are added source-language (en) only.

* Fix geohash-DM caption and placeholder

Two carve/review follow-ups:

- The privacy caption showed "private conversation" for geohash DMs,
  implying they are not encrypted — but geohash DMs are NIP-17
  gift-wrapped (always end-to-end encrypted), they just carry no Noise
  session status. Show the encrypted caption for geohash DMs and for
  secured Noise sessions; the pre-secured wording now applies only while
  a mesh handshake is still in progress.
- The private-chat placeholder prepended "@" to the partner name, which
  for a geohash DM (whose display name is already "#geohash/@name")
  produced a doubled "@". The "@" is now added only for mesh nicknames.

* Make the DM header orange wash visible in the matrix theme

The 6% orange background was chained after .themedSurface(), so in the
default matrix theme (whose themedSurface paints an opaque background)
the wash sat behind the surface and never rendered — it was only
visible in liquid glass. Apply the orange tint before .themedSurface()
so it layers in front of the themed background.

* Align DM lock glyph across text and media rows; keep header wash visible under glass

Media rows in a private conversation now get the same leading lock
glyph as text rows, so left edges line up instead of misaligning by
the glyph's width. The DM header's orange wash gets a higher opacity
under the liquid-glass theme, where themedSurface() adds no opaque
backing and 6% orange disappears into the backdrop gradient. Also
drops the dead sender != "system" guard in TextMessageView — system
messages are routed to systemMessageRow before this view is built.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Remove orphaned content.input.message_placeholder from the string catalog

The destination-stating placeholders replaced its last code reference;
nothing on the branch resolves this key anymore.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <212554440+jackjackbits@users.noreply.github.com>
Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchat/Views/ContentSheetViews.swift

@@ -363,6 +363,12 @@ private struct ContentPrivateChatSheetView: View {
                 .padding(.horizontal, 16)
                 .padding(.top, 10)
                 .padding(.bottom, 12)
+                // Orange tint before themedSurface so it layers in front of the
+                // (opaque, in matrix) themed background rather than behind it.
+                // Glass has no opaque backing — themedSurface is a no-op there,
+                // so the wash needs more opacity to read over the backdrop
+                // gradient's blue/purple glows.
+                .background(Color.orange.opacity(theme.usesGlassChrome ? 0.14 : 0.06))
                 .themedSurface()
             }
 
@@ -385,6 +391,8 @@ private struct ContentPrivateChatSheetView: View {
                 Divider()
             }
 
+            privacyCaption
+
             #if os(iOS)
             ContentComposerView(
                 messageText: $messageText,
@@ -421,6 +429,41 @@ private struct ContentPrivateChatSheetView: View {
                 }
         )
     }
+
+    /// Persistent one-line reminder that this composer feeds a private
+    /// conversation — the DM sheet otherwise renders identically to the
+    /// public timeline. Claims end-to-end encryption only once the session
+    /// is actually secured.
+    private var privacyCaption: some View {
+        HStack(spacing: 5) {
+            Image(systemName: "lock.fill")
+                .font(.bitchatSystem(size: 9))
+            Text(verbatim: privacyCaptionText)
+                .bitchatFont(size: 11, weight: .medium)
+        }
+        .foregroundColor(Color.orange)
+        .frame(maxWidth: .infinity)
+        .padding(.vertical, 4)
+        .background(Color.orange.opacity(0.08))
+        .accessibilityElement(children: .combine)
+    }
+
+    private var privacyCaptionText: String {
+        // Geohash DMs are NIP-17 gift-wrapped — always end-to-end encrypted,
+        // even though they carry no Noise session status. Mesh DMs earn the
+        // "encrypted" claim only once the Noise handshake has secured.
+        let isGeoDM = privateConversationModel.selectedPeerID?.isGeoDM == true
+        let noiseSecured: Bool = {
+            switch privateConversationModel.selectedHeaderState?.encryptionStatus {
+            case .noiseSecured, .noiseVerified: return true
+            default: return false
+            }
+        }()
+        if isGeoDM || noiseSecured {
+            return String(localized: "content.private.caption_encrypted", comment: "Caption above the private chat composer once the session is end-to-end encrypted")
+        }
+        return String(localized: "content.private.caption", comment: "Caption above the private chat composer before encryption is established")
+    }
 }
 
 private struct ContentPrivateHeaderInfoButton: View {