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/tool-button.slint

@@ -0,0 +1,33 @@
+/// TEMPORARY AI GENERATED FRONTEND \\\
+///   NOT TO BE USED IN PRODUCTION  \\\
+
+import { Theme } from "../theme.slint";
+import { Icon } from "icon.slint";
+
+// Small square icon button used in headers and hover toolbars.
+export component ToolButton inherits Rectangle {
+    in property <image> glyph;
+    in property <color> tint: Theme.text-muted;
+    in property <bool> active: false;
+    callback clicked();
+
+    width: 32px;
+    height: 28px;
+    border-radius: 4px;
+    background: touch.has-hover ? Theme.selected-bg : transparent;
+
+    Icon {
+        source: root.glyph;
+        icon-size: 18px;
+        tint: root.active || touch.has-hover ? Theme.text-header : root.tint;
+        x: (parent.width - self.width) / 2;
+        y: (parent.height - self.height) / 2;
+    }
+
+    touch := TouchArea {
+        mouse-cursor: pointer;
+        clicked => {
+            root.clicked();
+        }
+    }
+}