feat: implement client backend

This includes temporary AI-generated frontend scaffolding, none of this will be used in production. It was just used during development for the backend.

ui/components/avatar.slint

@@ -0,0 +1,26 @@
+/// TEMPORARY AI GENERATED FRONTEND \\\
+///   NOT TO BE USED IN PRODUCTION  \\\
+
+import { Theme } from "../theme.slint";
+
+// Coloured circle with an initial. Real avatar images (mxc:// media) are a
+// planned follow-up; this is also the fallback when a user has no avatar.
+export component Avatar inherits Rectangle {
+    in property <string> initial;
+    in property <color> tint: Theme.accent;
+    in property <length> diameter: 40px;
+
+    width: diameter;
+    height: diameter;
+    border-radius: diameter / 2;
+    background: tint;
+
+    Text {
+        text: root.initial;
+        color: white;
+        font-size: root.diameter * 0.42;
+        font-weight: 600;
+        horizontal-alignment: center;
+        vertical-alignment: center;
+    }
+}