feat(quickshell): add Manjaro distro icon support

Add manjaro-symbolic.svg (from font-logos, Unlicense) and map
the 'manjaro' distro ID to it in SystemInfo.qml so the sidebar
displays the Manjaro logo instead of the generic Linux icon.

dots/.config/quickshell/ii/assets/icons/manjaro-symbolic.svg

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns="http://www.w3.org/2000/svg"
+   width="200"
+   height="200"
+   viewBox="0 0 200 200">
+  <g transform="translate(222.41168,-236.90015)">
+    <rect width="58.534939" height="200" x="-80.946617" y="236.90016" />
+    <rect width="58.534939" height="129.26881" x="-151.68127" y="307.63138" />
+    <path transform="translate(-222.41168,236.90015)"
+          d="M 0 0 L 0 200 L 58.535156 200 L 58.535156 58.535156 L 129.26562 58.535156 L 129.26562 0 L 58.535156 0 L 20.765625 0 L 0 0 z " />
+  </g>
+</svg>

dots/.config/quickshell/ii/services/SystemInfo.qml

@@ -60,6 +60,7 @@ Singleton {
             switch (distroId) {
                 case "artix":
                 case "arch": distroIcon = "arch-symbolic"; break;
+                case "manjaro": distroIcon = "manjaro-symbolic"; break;
                 case "endeavouros": distroIcon = "endeavouros-symbolic"; break;
                 case "cachyos": distroIcon = "cachyos-symbolic"; break;
                 case "nixos": distroIcon = "nixos-symbolic"; break;