feat(icons): add sidebar expanding icon

src/assets/icons/sidebar-expand.svg

@@ -0,0 +1,38 @@
+<!--
+Copyright 2026 Seekra
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="24" height="24">
+    <path
+        stroke="currentColor"
+        stroke-width="2"
+        fill="none"
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        d="
+            M6 4
+            h12
+            a4 4 0 0 1 4 4
+            v8
+            a4 4 0 0 1 -4 4
+            h-12
+            a4 4 0 0 1 -4 -4
+            v-8
+            a4 4 0 0 1 4 -4
+            m2 0
+            v16
+        "
+    />
+</svg>