feat: add AppImage build pipeline with desktop integration and dependency bundling

Implement full AppImage packaging support including AppRun entry point, .desktop launcher, icon asset, and recursive shared library collection via collect_so_files.sh. The Makefile build target now generates a portable Linux executable by assembling the directory structure, copying the binary to AppImage/usr/bin/r, running the dependency collector, and invoking appimagetool to produce a self-contained AppImage binary. Also update .gitignore to exclude the AppImage build directory and add shell scripts to the ignore list.

collect_so_files.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+# Script: collect_so_files.sh
+
+BINARY="AppImage/usr/bin/r"
+LIB_DIR="AppImage/usr/lib"
+mkdir -p "$LIB_DIR"
+
+# Function to copy a library and its dependencies
+copy_with_deps() {
+    local lib="$1"
+    if [ -f "$lib" ] && [ ! -f "$LIB_DIR/$(basename "$lib")" ]; then
+        cp "$lib" "$LIB_DIR/"
+        echo "Copied: $lib"
+        # Recursively check dependencies of this library
+        ldd "$lib" | grep -o '/[^ ]\+' | while read -r dep; do
+            if [ -f "$dep" ]; then
+                copy_with_deps "$dep"
+            fi
+        done
+    fi
+}
+
+# Start with the binary’s dependencies
+ldd "$BINARY" | grep -o '/[^ ]\+' | while read -r lib; do
+    copy_with_deps "$lib"
+done
+