Liquid Glass theme with in-app appearance switcher (#1337)

* Centralize UI theme colors into semantic ThemePalette tokens

Introduce AppTheme/ThemePalette (Utils/Theme.swift) with an environment
key and @ThemedPalette property wrapper, persisted via @AppStorage.
Views now resolve background/primary/secondary/accentBlue/alertRed/
divider tokens from the environment instead of computing colors inline,
removing the backgroundColor/textColor/secondaryTextColor prop-drilling
through the header, composer, and people-sheet hierarchy.

Matrix theme output is pixel-identical; this is groundwork for a
user-selectable theme switcher.

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

* Add liquid glass theme with in-app appearance switcher

Add a .liquidGlass AppTheme alongside the matrix terminal theme,
selectable from a one-line APPEARANCE row in the app info sheet
(persisted via @AppStorage, applies live).

Liquid glass renders system fonts and colors over a subtle gradient
backdrop, with the header and composer floating as Liquid Glass panels
(real .glassEffect() on iOS/macOS 26, compiler-gated with an
ultraThinMaterial fallback for older SDKs). The message list scrolls
underneath the chrome via safe-area insets, and all sheets share the
same backdrop and surface language. The matrix theme is unchanged.

Details:
- Theme is threaded through ChatMessageFormatter so message
  AttributedStrings switch font design per theme; the per-message
  format cache gains a variant key so themes never serve each other's
  cached strings
- New palette tokens: accent (interactive tint) and locationAccent
  (geohash green), replacing scattered hardcoded greens/blues in the
  voice note, waveform, verification, and people-sheet views
- Header controls get full-height tap targets and the people count
  becomes a real Button (previously a tap gesture on the cluster)
- CommandSuggestionsView renders nothing when empty instead of a
  zero-height view that pushed the composer input off-center
- New appearance strings localized for all 29 catalog languages

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

---------

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

bitchat/ViewModels/ChatViewModel.swift

@@ -139,6 +139,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
     }
     private var visibleMessagesCache: [BitchatMessage]?
     @Published var currentColorScheme: ColorScheme = .light
+    @Published var currentTheme: AppTheme = .matrix
     @Published var isConnected = false
     @Published var nickname: String = "" {
         didSet {
@@ -1257,13 +1258,13 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
     // MARK: - Message Formatting
 
     @MainActor
-    func formatMessageAsText(_ message: BitchatMessage, colorScheme: ColorScheme) -> AttributedString {
-        messageFormatter.formatMessageAsText(message, colorScheme: colorScheme)
+    func formatMessageAsText(_ message: BitchatMessage, colorScheme: ColorScheme, theme: AppTheme? = nil) -> AttributedString {
+        messageFormatter.formatMessageAsText(message, colorScheme: colorScheme, theme: theme ?? currentTheme)
     }
 
     @MainActor
-    func formatMessageHeader(_ message: BitchatMessage, colorScheme: ColorScheme) -> AttributedString {
-        messageFormatter.formatMessageHeader(message, colorScheme: colorScheme)
+    func formatMessageHeader(_ message: BitchatMessage, colorScheme: ColorScheme, theme: AppTheme? = nil) -> AttributedString {
+        messageFormatter.formatMessageHeader(message, colorScheme: colorScheme, theme: theme ?? currentTheme)
     }
 
     // MARK: - Noise Protocol Support