feat: Introduce swipe navigation between new Chat and Sidebar components and establish initial multi-platform project structure.

packages/shared/src/styles/themes.css

@@ -370,3 +370,43 @@
 
   --text-feedback-warning: hsl(38.455, 100%, 43.137%);
 }
+
+
+/* ============================================
+   MOBILE OVERRIDES – Dark theme only
+   Darker, more unified backgrounds when .is-mobile is active.
+   Override --bg-tertiary so inline styles using var(--bg-tertiary)
+   (e.g. .channel-list in Sidebar.jsx) also pick up the new color.
+   ============================================ */
+
+/* Override the variable so all var(--bg-tertiary) usages resolve to #1C1D22 */
+.theme-dark .is-mobile {
+  --bg-tertiary: #1C1D22;
+}
+
+/* Server list needs a different (darker) color than --bg-tertiary */
+.theme-dark .is-mobile .server-list {
+  background-color: #141318;
+}
+
+/* Remove borders on channel panel and DM view (inline styles, needs !important) */
+.theme-dark .is-mobile .channel-panel,
+.theme-dark .is-mobile .channel-list {
+  border-left: none !important;
+}
+
+/* Chat area/header use var(--bg-primary), not --bg-tertiary, so override explicitly */
+.theme-dark .is-mobile .chat-container,
+.theme-dark .is-mobile .chat-area,
+.theme-dark .is-mobile .chat-header,
+.theme-dark .is-mobile .chat-input-form {
+  background-color: #1C1D22;
+}
+
+.theme-dark .is-mobile .chat-header {
+  border-bottom: 1px solid var(--app-frame-border);
+}
+
+.theme-dark .is-mobile .chat-input-wrapper {
+  background-color: #26262E;
+}