Add Material 3 candidate window addon for Fcitx5

Fork of the classicui addon (Fcitx5 5.1.23) with a Material 3 look, spring
based animations and a right click action menu for candidates.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scripts/install.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# Installs the addon, the themes and an example config into your home
+# directory. Nothing outside $HOME is touched and the stock classicui stays
+# available.
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")/.." && pwd)
+work=${WORK_DIR:-$root/build}
+prefix=${PREFIX:-$HOME/.local/m3ui}
+data=${XDG_DATA_HOME:-$HOME/.local/share}/fcitx5
+config=${XDG_CONFIG_HOME:-$HOME/.config}/fcitx5
+
+# Going through cmake's install step strips the build tree rpath, otherwise the
+# addon would load a second copy of libFcitx5Core from the build directory.
+cmake -DCMAKE_INSTALL_PREFIX="$prefix" -P "$work/cmake/src/ui/m3ui/cmake_install.cmake"
+
+mkdir -p "$data/addon" "$data/themes" "$config/conf"
+cp "$prefix/share/fcitx5/addon/m3ui.conf" "$data/addon/m3ui.conf"
+cp -r "$root"/themes/* "$data/themes/"
+if [ ! -e "$config/conf/m3ui.conf" ]; then
+    cp "$root/config/m3ui.conf.example" "$config/conf/m3ui.conf"
+fi
+
+addondir=$(dirname "$(find "$prefix" -name libm3ui.so | head -1)")
+cat <<MSG
+Installed. Try it with:
+
+  FCITX_ADDON_DIRS=$addondir:\$(pkg-config --variable=addondir Fcitx5Core 2>/dev/null || echo /usr/lib64/fcitx5) fcitx5 -r -u m3ui
+
+Go back to the stock interface with:  fcitx5 -r
+MSG